Fix HIGH priority issues: unbounded queries, rate limiting, health checks

Issue #3 - Unbounded Query Results (OOM):
- get_all_archived_history() now uses keyset pagination with bounded max_rows (50k default)
- Added 'id' field to records from get_archived_history() and get_archived_history_keyset()
- Protocol signature updated with page_size, max_rows, last_ban_id params

Issue #7 - Docker Health Check Fails:
- Added curl to Dockerfile.backend runtime image
- HEALTHCHECK now uses 'curl -f http://localhost:8000/api/health'
- compose.prod.yml: increased start_period to 40s, timeout to 10s
- Frontend healthcheck proxies to backend /api/health

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/models/blocklist_domain.py

@@ -0,0 +1,108 @@
+"""Blocklist domain models.
+
+Internal domain-focused models used by blocklist_service. These represent the
+business domain layer and are independent of HTTP response shapes.
+
+Response models are defined in `app.models.blocklist` and mappers convert domain
+models to response models at the router boundary.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from enum import StrEnum
+
+
+@dataclass(frozen=True)
+class DomainBlocklistSource:
+    """Blocklist source definition (domain model)."""
+
+    id: int
+    name: str
+    url: str
+    enabled: bool
+    created_at: str
+    updated_at: str
+
+
+@dataclass(frozen=True)
+class DomainImportLogEntry:
+    """A single blocklist import run record (domain model)."""
+
+    id: int
+    source_id: int | None
+    source_url: str
+    timestamp: str
+    ips_imported: int
+    ips_skipped: int
+    errors: str | None
+
+
+@dataclass(frozen=True)
+class DomainImportLogList:
+    """Paginated list of import log entries (domain model)."""
+
+    items: list[DomainImportLogEntry]
+    total: int
+    page: int
+    page_size: int
+
+
+class DomainScheduleFrequency(StrEnum):
+    """Available import schedule frequency presets (domain model)."""
+
+    hourly = "hourly"
+    daily = "daily"
+    weekly = "weekly"
+
+
+@dataclass(frozen=True)
+class DomainScheduleConfig:
+    """Import schedule configuration (domain model)."""
+
+    frequency: DomainScheduleFrequency
+    interval_hours: int = 24
+    hour: int = 3
+    minute: int = 0
+    day_of_week: int = 0
+
+
+@dataclass(frozen=True)
+class DomainScheduleInfo:
+    """Current schedule configuration with runtime metadata (domain model)."""
+
+    config: DomainScheduleConfig
+    next_run_at: str | None = None
+    last_run_at: str | None = None
+    last_run_errors: bool | None = None
+
+
+@dataclass(frozen=True)
+class DomainPreviewResult:
+    """Result of previewing a blocklist URL (domain model)."""
+
+    entries: list[str]
+    total_lines: int
+    valid_count: int
+    skipped_count: int
+
+
+@dataclass(frozen=True)
+class DomainImportSourceResult:
+    """Result of importing a single blocklist source (domain model)."""
+
+    source_id: int | None
+    source_url: str
+    ips_imported: int
+    ips_skipped: int
+    error: str | None
+
+
+@dataclass(frozen=True)
+class DomainImportRunResult:
+    """Aggregated result from a full import run (domain model)."""
+
+    results: list[DomainImportSourceResult]
+    total_imported: int
+    total_skipped: int
+    errors_count: int