fix(copilot-acp): tighten deprecation detection + sharpen GitHub Models 413 hint

Follow-up improvements on top of @konsisumer's cherry-picked fix for #10648:

1. Deprecation patterns required BOTH a product fingerprint ('gh-copilot') and
   a deprecation marker. The previous list included 'copilot-cli' and bare
   'deprecation', which would false-positive on stderr from the NEW
   @github/copilot CLI — whose repo is literally github.com/github/copilot-cli
   and which legitimately surfaces those substrings in its own messages.

2. Replace the deprecation hint. The user in #10648 installed
   'gh extension install github/gh-copilot' (the deprecated extension)
   thinking that's what ACP mode uses, when ACP actually spawns the new
   'copilot' binary from '@github/copilot'. The hint now points users at the
   correct install command ('npm install -g @github/copilot') with the new
   CLI's repo URL, and demotes provider-switching to a fallback alternative.

3. Change _URL_TO_PROVIDER value for models.inference.ai.azure.com from the
   'github-models' alias to the canonical 'copilot' provider id, matching the
   convention used by every other entry in the table.

4. Sharpen the 413 hint message. The free tier's ~8K cap is below the
   system-prompt floor, so this endpoint is fundamentally incompatible with
   an agentic loop — not a 'use a different URL' problem.

Tests:
- New parametrized false-positive coverage for the new CLI's stderr shape.
- Updated assertion to require canonical 'copilot' provider mapping.
- All 14 deprecation/URL tests pass.

agent/model_metadata.py

@@ -358,7 +358,12 @@ _URL_TO_PROVIDER: Dict[str, str] = {
     "api.deepseek.com": "deepseek",
     "api.githubcopilot.com": "copilot",
     "models.github.ai": "copilot",
-    "models.inference.ai.azure.com": "github-models",
+    # GitHub Models free tier (Azure-hosted prototyping endpoint) — same
+    # canonical provider as the Copilot API.  Hard per-request token cap
+    # (often 8K) makes it unusable for Hermes' system prompt, but mapping
+    # it here lets us recognize the endpoint and emit a targeted hint
+    # instead of falling through the unknown-custom-endpoint path.
+    "models.inference.ai.azure.com": "copilot",
     "api.fireworks.ai": "fireworks",
     "opencode.ai": "opencode-go",
     "api.x.ai": "xai",