fix(cli): spawn sibling fbuild-daemon binary, not bare PATH lookup (#830)

[zackees]

Problem

When a venv-installed fbuild CLI does daemon restart, the previous code bare-spawned "fbuild-daemon" and let the OS PATH lookup pick the binary. On Windows that picked up the user's global %USERPROFILE%\.local\bin\fbuild-daemon.exe from a prior system-wide install, leaving a venv 2.3.13 CLI silently restarting a 2.2.27 daemon. The user thinks they're testing fresh code; they aren't.

Repro from #830:

.venv\Scripts\fbuild.exe --version          # fbuild 2.3.13
.venv\Scripts\fbuild.exe daemon restart
.venv\Scripts\fbuild.exe daemon status      # Version: 2.2.27  Path: ~\.local\bin\fbuild-daemon.exe

Fix

Reuse the existing daemon_executable_hint() in spawn_daemon_process, which already checks for a fbuild-daemon (or .exe) binary in the same directory as the running fbuild CLI before falling back to the bare name (and thus PATH). The hint was already used by the info / status surfaces — now spawn agrees with them, so all three views of "which daemon binary is in play" stay consistent.

Also improve the spawn-failure error message to include the resolved path so the next person hitting an install-layout issue sees what was actually attempted, not just a generic PATH suggestion.

Verification

• soldr cargo check -p fbuild-cli clean
• soldr cargo clippy -p fbuild-cli --all-targets -- -D warnings clean

(daemon_executable_hint depends on std::env::current_exe(), which is hard to unit-test without a refactor; the function itself is small and was already covered by being the info-path's primary lookup.)

Closes #830

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📥 Commits

Reviewing files that changed from the base of the PR and between 1450a9c and da42039.

📒 Files selected for processing (1)

• crates/fbuild-cli/src/daemon_client.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/830-spawn-sibling-daemon-binary-v2

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