fix(acp): preserve explicit model providers

[BROCCOLO1D]

Summary

• Preserve explicit ACP provider:model selections instead of running provider auto-detection over them.
• Refs [Bug]: ACP session/set_model reroutes explicit anthropic:claude-sonnet-5 to OpenRouter ("No LLM provider configured") #59089.

Why

• session/set_model could parse anthropic:claude-sonnet-5 correctly, then immediately re-run detect_provider_for_model because the parsed provider matched the current provider.
• For new Anthropic model IDs that OpenRouter also indexes, that fallback can silently rewrite the provider to openrouter and fail sessions without OpenRouter credentials.

Changes

• acp_adapter/server.py: track provider-qualified ACP model inputs and skip provider auto-detection for explicit provider selections; also normalize current-provider slash form like anthropic/claude-sonnet-5 for ACP callers.
• tests/acp_adapter/test_acp_commands.py: cover explicit colon and current-provider slash selections, plus the unchanged bare-model auto-detection path.

Validation

• python -m pytest tests/acp_adapter/test_acp_commands.py -q -o 'addopts=' (7 passed)
• python -m py_compile acp_adapter/server.py
• git diff --check

Scope

• In scope: ACP session/set_model provider resolution for explicit provider-qualified model inputs.
• Out of scope: broader /model slash-command/provider auto-detection behavior tracked by related issues.

[teknium1]

Thanks for the focused ACP fix. Current origin/main still parses the requested model and then re-runs provider detection when target_provider == current_provider (acp_adapter/server.py:654-658), so an explicit current-provider selection can be overwritten by the OpenRouter fallback (hermes_cli/models.py:2076-2091).

The PR guards that fallback only for recognized explicit provider prefixes, preserves bare-model autodetection, and updates the shared resolver used by both ACP session/set_model and /model (acp_adapter/server.py:1772-1780, 1999-2017).

This is an automated hermes-sweeper review.