fix: stop draining queue on /clear (remove SessionEnd shim) (#2136)

* fix: stop draining queue on /clear (and on every other SessionEnd)

The SessionEnd hook was wired to session-complete on Claude Code, Gemini
CLI, the transcripts processor, the OpenCode plugin, and OpenClaw. All of
those paths called POST /api/sessions/complete, which marked the session
completed and abandoned every still-pending observation in the queue.

So typing /clear (or logging out, or quitting) wiped in-flight work that
the worker was perfectly happy to keep processing on its own.

Removed the entire shim:
- Deleted SessionEnd hook block in plugin/hooks/hooks.json
- Deleted src/cli/handlers/session-complete.ts and its registry entry
- Deleted POST /api/sessions/complete route + Zod schema in SessionRoutes
- Removed call from transcripts processor handleSessionEnd
- Removed call from opencode-plugin session.deleted handler
- Removed Gemini SessionEnd → session-complete mapping
- Removed openclaw scheduleSessionComplete + completionDelayMs + timer state
- Updated tests + comments accordingly

Explicit user-initiated deletion (DELETE /api/sessions/:id and
POST /api/sessions/:sessionDbId/complete from the viewer UI) still works
via SessionCompletionHandler.completeByDbId — that's the only path that
should drain the queue.

The worker self-completes via its SDK-agent generator's finally-block, so
no external completion call is needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: clarify opencode-plugin session.deleted is in-memory cleanup only

Greptile P2: file-level header still implied session.deleted called the
worker. Now it only cleans up the local contentSessionIdsByOpenCodeSessionId
map; worker self-completes via the SDK-agent generator finally-block.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/gemini-cli-compat.test.ts

@@ -39,10 +39,10 @@ describe('GeminiCliHooksInstaller - event mapping', () => {
     expect(src).toContain("'SessionStart': 'context'");
   });
 
-  it('should map SessionEnd to session-complete (unchanged)', async () => {
+  it('should not map SessionEnd (worker self-completes; /clear must not drain queue)', async () => {
     const { readFileSync } = await import('fs');
     const src = readFileSync('src/services/integrations/GeminiCliHooksInstaller.ts', 'utf-8');
-    expect(src).toContain("'SessionEnd': 'session-complete'");
+    expect(src).not.toContain("'SessionEnd':");
   });
 });