fix: security hardening, stability fixes, and audit logging

[Noopy420]

Summary

• Security: Fix command injection in git operations — Branch names are now validated against shell metacharacters, and all arguments are shell-escaped before passing to exec(). Uses git worktree list --porcelain for reliable parsing that handles paths with spaces.
• Stability: Cap shell output buffer at 10 MB — Prevents OOM crashes when a shell command produces infinite output (e.g., yes, cat /dev/urandom). Appends a truncation notice when the limit is hit.
• Stability: Per-channel query isolation — Replaces the single global activeQuery variable with a Map<channelId, Query> so concurrent /claude commands from different channels don't overwrite each other's sessions.
• Stability: 10-minute timeout on Claude SDK queries — Wraps executeWithErrorHandling() with Promise.race() to abort if the SDK hangs indefinitely.
• Stability: Discord embed size validation — Adds safeTruncate() to enforce Discord's 4096-char embed description limit, preventing API errors on large Claude responses.
• Fix: .env parsing handles quoted values with = — Values like SECRET="a=b=c" now parse correctly. Also handles escape sequences in double-quoted values and inline comments in unquoted values.
• Fix: Crash recovery is now functional — recoverShellProcess(), recoverWorktreeProcess(), and recoverClaudeProcess() now properly clean up resources with structured logging instead of being stubs.
• Feature: Auto-archive inactive session threads — The cleanup() method now archives Discord threads before removing them from internal state, keeping the server tidy. Addresses Feature Req: better session management #19.
• Feature: Audit logger — New util/audit-logger.ts provides in-memory + JSONL file audit logging for all bot commands, including user, command, cost, and duration tracking.

Test plan

• Verify bot starts correctly with existing .env configuration
• Test /worktree with valid branch names (should work as before)
• Test /worktree with malicious branch names like ; rm -rf / (should be rejected)
• Test /shell with a command that produces large output (should truncate at 10 MB)
• Test concurrent /claude commands in different channels (should not interfere)
• Verify Claude responses with long output render correctly in Discord embeds
• Test .env file with SECRET="key=value" format (should parse correctly)
• Verify inactive session threads get archived during periodic cleanup

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