fix(worktree): address PR review — schema guard, startup adoption, query parity

Addresses six CodeRabbit/Greptile findings on PR #2052:

- Schema guard in adoptMergedWorktrees probes for merged_into_project
  columns before preparing statements; returns early when absent so first
  boot after upgrade (pre-migration) doesn't silently fail.

- Startup adoption now iterates distinct cwds from pending_messages and
  dedupes via resolveMainRepoPath — the worker daemon runs with
  cwd=plugin scripts dir, so process.cwd() fallback was a no-op.

- ObservationCompiler single-project queries (queryObservations /
  querySummaries) OR merged_into_project into WHERE so injected context
  surfaces adopted worktree rows, matching the Multi variants.

- SessionStore constructor now calls ensureMergedIntoProjectColumns so
  bundled artifacts (context-generator.cjs) that embed SessionStore get
  the merged_into_project column on DBs that only went through the
  bundled migration chain.

- OBSERVER_SESSIONS_PROJECT constant is now derived from
  basename(OBSERVER_SESSIONS_DIR) and used across PaginationHelper,
  SessionStore, and timeline queries instead of hardcoded strings.

- Corrected misleading Chroma retry docstring in WorktreeAdoption to
  match actual behavior (no auto-retry once SQL commits).

src/services/context/ObservationCompiler.ts

@@ -52,7 +52,7 @@ export function queryObservations(
       o.created_at_epoch
     FROM observations o
     LEFT JOIN sdk_sessions s ON o.memory_session_id = s.memory_session_id
-    WHERE o.project = ?
+    WHERE (o.project = ? OR o.merged_into_project = ?)
       AND type IN (${typePlaceholders})
       AND EXISTS (
         SELECT 1 FROM json_each(o.concepts)
@@ -62,6 +62,7 @@ export function queryObservations(
     ORDER BY o.created_at_epoch DESC
     LIMIT ?
   `).all(
+    project,
     project,
     ...typeArray,
     ...conceptArray,
@@ -93,12 +94,12 @@ export function querySummaries(
       ss.created_at_epoch
     FROM session_summaries ss
     LEFT JOIN sdk_sessions s ON ss.memory_session_id = s.memory_session_id
-    WHERE ss.project = ?
+    WHERE (ss.project = ? OR ss.merged_into_project = ?)
       ${platformSource ? "AND COALESCE(s.platform_source, 'claude') = ?" : ''}
     ORDER BY ss.created_at_epoch DESC
     LIMIT ?
   `).all(
-    ...[project, ...(platformSource ? [platformSource] : []), config.sessionCount + SUMMARY_LOOKAHEAD]
+    ...[project, project, ...(platformSource ? [platformSource] : []), config.sessionCount + SUMMARY_LOOKAHEAD]
   ) as SessionSummary[];
 }