refactor: restructure to plugin/ + services/ layout and add per-turn bootstrap injection

- Migrate src/ → plugin/ (plugin/core/, plugin/web/, plugin/commands/)
  and src/mcp/ → services/ per OpenClaw plugin dev spec
- Add Gemini CLI backend (plugin/core/gemini/sdk-adapter.ts) with GEMINI.md
  system-prompt injection
- Inject bootstrap as stateless system prompt on every turn instead of
  first turn only: Claude via --system-prompt, Gemini via workspace/GEMINI.md;
  eliminates isFirstTurn branch, keeps skills in sync with OpenClaw snapshots
- Fix session-map-store defensive parsing (sessions ?? []) to handle bare {}
  reset files without crashing on .find()
- Add docs/TEST_FLOW.md with E2E test scenarios and expected outcomes
- Add docs/claude/BRIDGE_MODEL_FINDINGS.md with contractor-probe results

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/contractor-probe/openclaw.plugin.json

@@ -0,0 +1,8 @@
+{
+  "id": "contractor-probe",
+  "name": "Contractor Probe",
+  "version": "0.1.0",
+  "description": "Test plugin to inspect custom model provider payloads",
+  "main": "index.ts",
+  "configSchema": {}
+}