refactor(backend): clean up jail service, add error handling service

- Extract jail status/processing to helper functions
- Add error_handling.py service for centralized error handling
- Update config.py with validation and defaults
- Update .env.example with all config options
- Remove obsolete Tasks.md, add Service-Development.md
- Minor fixes across routers and services

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

backend/app/services/error_handling.py

@@ -0,0 +1,64 @@
+"""Error handling contracts for services.
+
+Defines the three allowed error handling patterns so callers know what to
+expect from any service method.
+
+Pattern Selection
+================
+- ABORT_ON_ERROR: Operations where failure must propagate (auth, writes, config changes)
+- RETURN_DEFAULT: Informational reads where partial data is acceptable
+- PARTIAL_RESULT: Operations on collections where some items may fail independently
+
+Switching patterns is a breaking change — document in changelog.
+"""
+
+from __future__ import annotations
+
+ABORT_ON_ERROR = "abort_on_error"
+"""Raise an exception. Router converts to HTTP. Use for auth, writes, state changes."""
+
+RETURN_DEFAULT = "return_default"
+"""Return empty result and log warning. Never raises. Use for informational reads."""
+
+PARTIAL_RESULT = "partial_result"
+"""Return (result, errors) tuple. Use for batch operations on collections."""
+
+
+class ServiceErrorContract:
+    """Documents the error handling pattern for a service or method.
+
+    Callers use this to understand how errors affect the return value:
+
+    ABORT_ON_ERROR
+        Raise an exception. Router handles it, converts to HTTP response.
+        Used for: authentication, authorization, write operations,
+        state changes, and any operation where partial success is meaningless.
+
+    RETURN_DEFAULT
+        Return empty/None result and log a warning. Caller gets a valid
+        result with no items, not an error.
+        Used for: informational reads (list, get) where infrastructure
+        unavailability should not block the UI.
+
+    PARTIAL_RESULT
+        Return a result that contains both successful items and a list
+        of errors. Caller decides what to do with each.
+        Used for: batch operations, multi-item fetches where one item
+        failing does not invalidate the rest.
+    """
+
+    ABORT_ON_ERROR = ABORT_ON_ERROR
+    RETURN_DEFAULT = RETURN_DEFAULT
+    PARTIAL_RESULT = PARTIAL_RESULT
+
+    @classmethod
+    def doc(cls, pattern: str, *, since: str | None = None) -> str:
+        """Return a docstring fragment describing the error pattern."""
+        desc = {
+            ABORT_ON_ERROR: "Raises exceptions on error. Router handles conversion to HTTP.",
+            RETURN_DEFAULT: "Returns empty result and logs warning on error. Never raises.",
+            PARTIAL_RESULT: "Returns (result, errors) tuple. Errors collected, not raised.",
+        }[pattern]
+        if since:
+            return f"{desc} (Since: {since})"
+        return desc