Release v4.2.6: Critical bugfix for observation validation

Critical Bugfix:
- Fixed overly defensive observation validation blocking observations from being saved
- Parser now NEVER skips observations - always saves them
- Invalid or missing type defaults to "change" (generic catch-all type)
- Removed validation requiring title, subtitle, and narrative fields
- Prevents critical data loss - partial observations better than no observations

Impact:
- Before: Missing title, subtitle, OR narrative caused entire observation to be discarded
- After: ALL observations preserved regardless of field completeness
- Even partial observations contain valuable data: concepts, files_read, files_modified, facts
- LLMs make mistakes - system must be resilient and save everything
- Consistent with v4.2.5 summary fix

Technical changes:
- Updated src/sdk/parser.ts:52-67 to never skip observations
- Uses "change" as fallback type for invalid/missing types (no schema change)
- Updated ParsedObservation interface to allow null for title, subtitle, narrative
- Updated SessionStore.storeObservation signature to accept nullable fields
- Updated built worker-service.cjs
- Bumped version to 4.2.6 in all metadata files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/services/sqlite/SessionStore.ts

@@ -903,10 +903,10 @@ export class SessionStore {
     project: string,
     observation: {
       type: string;
-      title: string;
-      subtitle: string;
+      title: string | null;
+      subtitle: string | null;
       facts: string[];
-      narrative: string;
+      narrative: string | null;
       concepts: string[];
       files_read: string[];
       files_modified: string[];