fix(ttp): /api/v1/ttp/rules returns the live rule catalogue

The endpoint was a contract-phase stub returning `[]` even though the
RuleStore loaded all 58 YAML rules at worker startup. UI saw an empty
table; operators couldn't tell whether anything was wired up.

- `api_list_rules` now calls `get_rule_store().load_compiled()` and
  serializes each CompiledRule + its operational state into a
  RuleCatalogueRow. Sorted by rule_id for stable golden snapshots.
- Add `description: str` to RuleSchema (pydantic) and CompiledRule
  (NamedTuple, defaulted) + propagate through `_compile_one` so the
  catalogue surfaces the human-readable YAML description, not just
  the slug-style `name`.
- Update `tests/ttp/test_rule_engine.py` _fields assertion for the
  new column; new `tests/api/ttp/test_rules_catalogue.py` pins the
  catalogue contents (R0001/R0014 presence, row shape, sort order).

Worker behaviour is unchanged: it was already loading rules
correctly. This is purely a read-side wiring fix on the operator API.

decnet/ttp/impl/rule_engine.py

@@ -122,6 +122,11 @@ class CompiledRule(NamedTuple):
     evidence_fields: tuple[str, ...]
     #: Operational state stamped in by the store at compile time.
     state: "RuleState"
+    #: Human-readable description from the YAML rule. Surfaced in the
+    #: ``GET /api/v1/ttp/rules`` catalogue. Default empty so existing
+    #: callers constructing ``CompiledRule`` (lifter unit tests) keep
+    #: working without churn.
+    description: str = ""
 
 
 class RuleSchema(BaseModel):
@@ -137,6 +142,7 @@ class RuleSchema(BaseModel):
     rule_id: str
     rule_version: int
     name: str
+    description: str = ""
     applies_to: list[str]
     match: dict[str, Any]
     #: ``[{"tactic": "TA0007", "technique_id": "T1083",

decnet/ttp/store/impl/filesystem.py

@@ -181,6 +181,7 @@ def _compile_one(parsed: RuleSchema, state: RuleState) -> CompiledRule:
         emits=tuple(emits),
         evidence_fields=tuple(parsed.evidence_fields),
         state=state,
+        description=parsed.description,
     )