feat(backend): add conf-file parser and extend config models

- Add conffile_parser.py: reads, writes and manipulates fail2ban .conf
  files while preserving comments and section structure
- Extend config models with ActionConfig, FilterConfig, ConfFileContent,
  and related Pydantic schemas for jails, actions, and filters

backend/app/models/config.py

@@ -267,3 +267,183 @@ class MapColorThresholdsUpdate(BaseModel):
         ..., gt=0, description="Ban count for yellow."
     )
     threshold_low: int = Field(..., gt=0, description="Ban count for green.")
+
+
+# ---------------------------------------------------------------------------
+# Parsed filter file models
+# ---------------------------------------------------------------------------
+
+
+class FilterConfig(BaseModel):
+    """Structured representation of a ``filter.d/*.conf`` file."""
+
+    model_config = ConfigDict(strict=True)
+
+    name: str = Field(..., description="Filter base name, e.g. ``sshd``.")
+    filename: str = Field(..., description="Actual filename, e.g. ``sshd.conf``.")
+    # [INCLUDES]
+    before: str | None = Field(default=None, description="Included file read before this one.")
+    after: str | None = Field(default=None, description="Included file read after this one.")
+    # [DEFAULT] — free-form key=value pairs
+    variables: dict[str, str] = Field(
+        default_factory=dict,
+        description="Free-form ``[DEFAULT]`` section variables.",
+    )
+    # [Definition]
+    prefregex: str | None = Field(
+        default=None,
+        description="Prefix regex prepended to every failregex.",
+    )
+    failregex: list[str] = Field(
+        default_factory=list,
+        description="Failure detection regex patterns (one per list entry).",
+    )
+    ignoreregex: list[str] = Field(
+        default_factory=list,
+        description="Regex patterns that bypass ban logic.",
+    )
+    maxlines: int | None = Field(
+        default=None,
+        description="Maximum number of log lines accumulated for a single match attempt.",
+    )
+    datepattern: str | None = Field(
+        default=None,
+        description="Custom date-parsing pattern, or ``None`` for auto-detect.",
+    )
+    journalmatch: str | None = Field(
+        default=None,
+        description="Systemd journal match expression.",
+    )
+
+
+class FilterConfigUpdate(BaseModel):
+    """Partial update payload for a parsed filter file.
+
+    Only explicitly set (non-``None``) fields are written back.
+    """
+
+    model_config = ConfigDict(strict=True)
+
+    before: str | None = Field(default=None)
+    after: str | None = Field(default=None)
+    variables: dict[str, str] | None = Field(default=None)
+    prefregex: str | None = Field(default=None)
+    failregex: list[str] | None = Field(default=None)
+    ignoreregex: list[str] | None = Field(default=None)
+    maxlines: int | None = Field(default=None)
+    datepattern: str | None = Field(default=None)
+    journalmatch: str | None = Field(default=None)
+
+
+# ---------------------------------------------------------------------------
+# Parsed action file models
+# ---------------------------------------------------------------------------
+
+
+class ActionConfig(BaseModel):
+    """Structured representation of an ``action.d/*.conf`` file."""
+
+    model_config = ConfigDict(strict=True)
+
+    name: str = Field(..., description="Action base name, e.g. ``iptables``.")
+    filename: str = Field(..., description="Actual filename, e.g. ``iptables.conf``.")
+    # [INCLUDES]
+    before: str | None = Field(default=None)
+    after: str | None = Field(default=None)
+    # [Definition] — well-known lifecycle commands
+    actionstart: str | None = Field(
+        default=None,
+        description="Executed at jail start or first ban.",
+    )
+    actionstop: str | None = Field(
+        default=None,
+        description="Executed at jail stop.",
+    )
+    actioncheck: str | None = Field(
+        default=None,
+        description="Executed before each ban.",
+    )
+    actionban: str | None = Field(
+        default=None,
+        description="Executed to ban an IP.  Tags: ``<ip>``, ``<name>``, ``<port>``.",
+    )
+    actionunban: str | None = Field(
+        default=None,
+        description="Executed to unban an IP.",
+    )
+    actionflush: str | None = Field(
+        default=None,
+        description="Executed to flush all bans on shutdown.",
+    )
+    # [Definition] — extra variables not covered by the well-known keys
+    definition_vars: dict[str, str] = Field(
+        default_factory=dict,
+        description="Additional ``[Definition]`` variables.",
+    )
+    # [Init] — runtime-configurable parameters
+    init_vars: dict[str, str] = Field(
+        default_factory=dict,
+        description="Runtime parameters that can be overridden per jail.",
+    )
+
+
+class ActionConfigUpdate(BaseModel):
+    """Partial update payload for a parsed action file."""
+
+    model_config = ConfigDict(strict=True)
+
+    before: str | None = Field(default=None)
+    after: str | None = Field(default=None)
+    actionstart: str | None = Field(default=None)
+    actionstop: str | None = Field(default=None)
+    actioncheck: str | None = Field(default=None)
+    actionban: str | None = Field(default=None)
+    actionunban: str | None = Field(default=None)
+    actionflush: str | None = Field(default=None)
+    definition_vars: dict[str, str] | None = Field(default=None)
+    init_vars: dict[str, str] | None = Field(default=None)
+
+
+# ---------------------------------------------------------------------------
+# Jail file config models (Task 6.1)
+# ---------------------------------------------------------------------------
+
+
+class JailSectionConfig(BaseModel):
+    """Settings within a single [jailname] section of a jail.d file."""
+
+    model_config = ConfigDict(strict=True)
+
+    enabled: bool | None = Field(default=None, description="Whether this jail is enabled.")
+    port: str | None = Field(default=None, description="Port(s) to monitor (e.g. 'ssh' or '22,2222').")
+    filter: str | None = Field(default=None, description="Filter name to use (e.g. 'sshd').")
+    logpath: list[str] = Field(default_factory=list, description="Log file paths to monitor.")
+    maxretry: int | None = Field(default=None, ge=1, description="Failures before banning.")
+    findtime: int | None = Field(default=None, ge=1, description="Time window in seconds for counting failures.")
+    bantime: int | None = Field(default=None, description="Ban duration in seconds. -1 for permanent.")
+    action: list[str] = Field(default_factory=list, description="Action references.")
+    backend: str | None = Field(default=None, description="Log monitoring backend.")
+    extra: dict[str, str] = Field(default_factory=dict, description="Additional settings not captured by named fields.")
+
+
+class JailFileConfig(BaseModel):
+    """Structured representation of a jail.d/*.conf file."""
+
+    model_config = ConfigDict(strict=True)
+
+    filename: str = Field(..., description="Filename including extension (e.g. 'sshd.conf').")
+    jails: dict[str, JailSectionConfig] = Field(
+        default_factory=dict,
+        description="Mapping of jail name → settings for each [section] in the file.",
+    )
+
+
+class JailFileConfigUpdate(BaseModel):
+    """Partial update payload for a jail.d file."""
+
+    model_config = ConfigDict(strict=True)
+
+    jails: dict[str, JailSectionConfig] | None = Field(
+        default=None,
+        description="Jail section updates. Only jails present in this dict are updated.",
+    )