fix(policy): Policy.extra=ignore so old persisted files load cleanly (#966)

Persisted tool_policy.json files from an earlier revision of this PR
carry default_action (since dropped) and rejected with ValidationError
on load — surfacing as 'Could not load policy: 500' when the user
clicked the per-tool gated toggle.

Predicate/Rule keep extra=forbid (typo catching at construction).

Author: kingpanther13

src/ha_mcp/policy/model.py

@@ -82,9 +82,15 @@ class Policy(BaseModel):
     The system is always "allow unless a rule matches; rule = require
     approval". There is no global deny/require-approval default — rules
     grant approval gates, nothing else.
+
+    ``extra="ignore"`` so policies persisted by an older version of this
+    PR (which may carry removed fields like ``default_action``) load
+    cleanly; the dropped fields are silently discarded on next save.
+    Predicate/Rule keep ``extra="forbid"`` since those are constructed
+    from UI / user-typed JSON where typos should fail loudly.
     """
 
-    model_config = ConfigDict(extra="forbid")
+    model_config = ConfigDict(extra="ignore")
 
     enabled: bool = False
     wait_seconds: int = Field(default=60, ge=5, le=600)