fix: compose model route overrides

[giscebot]

Summary

• compose every matching model route field by field instead of selecting one route object and stopping
• keep global action and complexity rules effective when a repository default overrides only thinking
• preserve repository-specific action, complexity, and intent rules as the most specific overrides
• document the layered resolution order and partial override semantics

Resolution order

Routes are applied from broad defaults to specific overrides:

1. global default
2. repository default
3. global intent, complexity, then action
4. repository intent, complexity, then action

Each layer replaces only the model or thinking field it defines. For example:

"gisce/github-agent-bridge": {
  "default": { "thinking": "xhigh" }
}

keeps OpenClaw's inherited model while global mechanical and sync_after_merge routes can still select their cheaper model and thinking level.

Validation

• pytest -q tests/test_policy.py — 22 passed
• pytest -q — 382 passed

Requested by: @ecarreras

[pilipilisbot]

Approved. I reviewed the model route composition change in policy.py, the policy reference update, and the added policy tests. The new overlay order preserves global defaults, lets repo defaults override only specified fields, then applies global intent/complexity/action and finally repo-specific overrides, which matches the documented behavior and the PR intent.

Checks run locally on head 83b3a28:

• pytest -q tests/test_policy.py: 22 passed
• pytest -q: 382 passed, 1 unrelated Starlette/httpx deprecation warning

CI is also green for dashboard and pytest on Python 3.11/3.12.