fix(acp): resolve npx agents from ~/.local/bin and trust the terminal probe

[Sma1lboy]

What does this PR do?

Hermes installed with the official installer (~/.local/bin/hermes, no npm hermes-agent) shows as not installed when codeg is launched from the GUI, and diagnostics report not_installed. Two causes, both in src-tauri/src/commands/acp.rs:

1. resolve_npx_command() and NpxCommandResolver::resolve_for_list() (the agent-list path) only check PATH and the npm global prefix. A GUI app's PATH usually lacks ~/.local/bin, so Hermes resolves to None. Binary agents already fall back to ~/.local/bin through resolve_system_agent_binary(); npx agents did not.
2. compute_verdict() only reaches terminal_only_path for an unresolved npx agent when db_version or detected_version is set. Both come from npm, so an install without an npm record falls through to not_installed, even when the terminal probe found the command.

Related Issue

Fixes #875

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)

Changes Made

• src-tauri/src/commands/acp.rs: resolve_npx_command() and NpxCommandResolver::resolve_for_list() now call resolve_system_agent_binary(cmd) (PATH, then ~/.local/bin) before the npm global prefix. The order is PATH → ~/.local/bin → npm prefix, so when both an official install and an npm copy exist, a GUI launch picks the official one, the same as a terminal launch where it is on PATH. This matches the launch preference described in the Hermes entry in acp/registry.rs.
• src-tauri/src/commands/acp.rs: in compute_verdict(), an unresolved npx agent with no npm record whose command resolves in the login shell now gets terminal_only_path instead of not_installed. The Node/npm checks still run first. The check sits before the adapter branch because the terminal probe looks up the agent's own command, so a hit means the adapter itself is installed. The existing npm-evidence branch is unchanged.
• Two unit tests:
  • npx_command_resolution_checks_local_bin_before_npm_prefix: with HOME pointed at a temp dir, both npx lookup paths find ~/.local/bin/<cmd>. The list path also has the same command in an npm prefix and still returns the ~/.local/bin one. Unix only.
  • verdict_terminal_only_path_without_npm_evidence.

How to Test

1. On macOS, install Hermes with the official installer so ~/.local/bin/hermes exists, and make sure the npm hermes-agent package is not installed.
2. Start codeg-server with a GUI-like PATH that has node/npm but not ~/.local/bin, e.g. PATH=<nvm node bin>:/usr/bin:/bin:/usr/sbin:/sbin, and an empty CODEG_DATA_DIR.
3. Call POST /api/acp_env_diagnostics with {"agentType":"hermes"}, plus acp_get_agent_status and acp_list_agents.

Result with Hermes 0.21.5 on macOS 15 (Apple Silicon), same environment for both builds:

	main (592131c)	this PR
hermes (resolve_npx_command)	NOT RESOLVED	~/.local/bin/hermes
command -v <cmd> (login shell)	~/.local/bin/hermes	~/.local/bin/hermes
verdict	not_installed	ok
status / list installed_version	null	0.21.5+5839.gbed0d53

The two new unit tests fail on main and pass on this branch.

Checklist

Code

• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate (fix: detect externally installed ACP agents #286 is an older, broader change in the same area)
• My PR contains only changes related to this fix
• cargo test --features test-utils --lib commands::acp passes
• cargo clippy -- -D warnings (desktop and server): see the note below
• I've added tests for my changes
• I've tested on my platform: macOS 15 (Apple Silicon)

Documentation & Housekeeping

• I've updated relevant documentation: N/A
• I've considered cross-platform impact (Windows, macOS): the ~/.local/bin lookup is the existing resolve_system_agent_binary(), including its .exe handling; the resolver test is unix only

Screenshots / Logs

• cargo test --features test-utils --lib commands::acp: all passed.
• Desktop and server cargo clippy ... -- -D warnings with Rust 1.96 report one error, clippy::nonminimal_bool at src/computer/helper/mod.rs:667. That line exists on main and is not touched here. With -A clippy::nonminimal_bool both are clean.
• cargo fmt --check already reports differences across the repo on main. Formatting acp.rs before and after this change gives the same diff as this PR, so the new lines are formatted.

[xintaofei]

codeg work task 289 is done — #888 (3 files, +107/-48).