refactor: decouple kild CLI from kild-daemon server embedding

[Wirasm]

Summary

• Make kild-daemon a standalone binary instead of embedding the server as a library dependency in the CLI crate
• CLI now spawns kild-daemon as a subprocess for both foreground (--foreground) and background modes
• Auto-start in kild-core discovers the daemon binary as a sibling executable (same pattern as kild-tmux-shim)
• Removes tokio and kild-daemon dependencies from the CLI crate

Test plan

• cargo fmt --check passes
• cargo clippy --all -- -D warnings passes (zero warnings)
• cargo test --all passes (all tests green)
• cargo build --all succeeds (both kild and kild-daemon binaries produced)
• Manual: kild daemon start starts daemon in background
• Manual: kild daemon start --foreground spawns kild-daemon with inherited stdio
• Manual: kild daemon stop / kild daemon status work unchanged
• Manual: auto-start triggers kild-daemon binary spawn

Closes #324

[Wirasm]

PR Review Summary

Critical Issues (1 found)

Agent	Issue	Location
code-reviewer	Binary discovery logic duplicated 3 times (autostart.rs, daemon.rs, handler.rs) — should be a shared utility	autostart.rs:31-47, daemon.rs:4-18, handler.rs

Important Issues (1 found)

Agent	Issue	Location
code-reviewer	CLI background daemon polling loop lacks child-process crash detection that autostart.rs has — could wait full 5s timeout when daemon crashes immediately	daemon.rs:74-85 vs autostart.rs:62-119

Suggestions (3 found)

Agent	Suggestion	Location
silent-failure-hunter	Add structured logging to kild-daemon/main.rs run() for config load vs runtime init vs server failures	main.rs:21-30
silent-failure-hunter	Log spawn success with PID before entering socket readiness loop	daemon.rs:62-67
silent-failure-hunter	Add debug logging inside CLI socket readiness loop for visibility	daemon.rs:74-85

Documentation Updates

• CLAUDE.md — Updated architecture section to reflect kild-daemon as standalone binary (committed to PR branch)

Strengths

• Clean decoupling — CLI no longer depends on tokio or kild-daemon crate
• Autostart binary discovery follows the same sibling-binary pattern as kild-tmux-shim
• Error messages include binary path and actionable guidance ("Run 'cargo build --all'")
• Autostart polling loop has excellent crash detection and differentiated timeout errors

Verdict: NEEDS FIXES

Recommended Actions

1. Extract binary discovery into a shared find_sibling_binary(name: &str) utility in kild-core (eliminates 3x duplication, also benefits existing shim discovery in handler.rs)
2. Consider adding child-process crash detection to CLI background daemon start loop (or document why it's intentionally simpler)
3. Optionally: add structured logging in daemon main.rs and spawn success events