[FEATURE] /forget slash command

[urbantech]

Summary

• Replaces the placeholder skills/forget/SKILL.md stub with a full production-ready implementation
• Numbered match presentation with stored dates for each candidate memory
• Granular selection: user types specific numbers (e.g. 1,2), all, or cancel — not just yes/no
• --type <type> flag to pre-filter matches by memory type before presenting
• --all nuclear option with hard double-confirmation (user must type DELETE in all caps)
• Project-scoped search via git remote get-url origin, falls back to unknown if not in a git repo
• Error handling when ZeroDB MCP tools are unavailable
• Expanded /forget section in skills/zerodb-memory-guide/SKILL.md to match the full flow

Test Plan

• /forget <query> — shows numbered results, waits for selection, deletes on confirm
• /forget <query> — "cancel" aborts with no deletions
• /forget --type convention <query> — only shows memories of the given type
• /forget --all — prompts with count, only proceeds on exact DELETE response
• /forget --all — any other response cancels with preservation message
• No ZeroDB connection — returns actionable error message
• Run outside git repo — falls back to unknown project, searches all memories

Risk / Rollback

Low risk — skill files only, no runtime code changes. Rollback: revert skills/forget/SKILL.md to the stub.

Closes #9