fix(agent): consult supports_vision override in auto-mode routing

The contributor PR (#17936) only patched the strip path in
`_model_supports_vision()`. The auto-mode router in
`agent/image_routing._lookup_supports_vision` still only read models.dev,
so a custom-provider model declared as vision-capable would still get its
images routed through vision_analyze in the default `agent.image_input_mode:
auto` setting. Users had to set both `supports_vision: true` AND
`image_input_mode: native` to bypass the text pipeline.

Single-knob behavior now: `supports_vision: true` alone is enough in auto
mode. The strip path and the routing path consult the same resolver.

- Extract override resolution into `_supports_vision_override()` in
  agent/image_routing.py and wire it into `_lookup_supports_vision()`.
- Refactor `run_agent._model_supports_vision` to call the same helper
  (DRY, single source of truth for the resolution order).
- Strict YAML boolean coercion: `supports_vision: "false"` (quoted —
  a common YAML mistake) no longer coerces to True via bool() truthiness.
  Recognised tokens: true/false/yes/no/on/off/1/0 plus real bools and 0/1.
  Unrecognised values return None and fall through to models.dev.
- Add @CNSeniorious000 to AUTHOR_MAP for release attribution.

Tests: 26 new (TestCoerceCapabilityBool, TestSupportsVisionOverride,
TestLookupSupportsVisionOverride, TestAutoModeRespectsOverride). Existing
contributor tests + image_routing + vision_native_fast_path +
native_image_buffer_isolation all green (92/92).

scripts/release.py

@@ -47,6 +47,7 @@ ACP_REGISTRY_MANIFEST = REPO_ROOT / "acp_registry" / "agent.json"
 AUTHOR_MAP = {
     # teknium (multiple emails)
     "teknium1@gmail.com": "teknium1",
+    "me@promplate.dev": "CNSeniorious000",
     "erhanyasarx@gmail.com": "erhnysr",
     "30366221+WorldWriter@users.noreply.github.com": "WorldWriter",
     "dafeng@DafengdeMacBook-Pro.local": "WorldWriter",