feat: agent auto-setup with interactive picker

[qdequele]

Summary

Makes memd setup agent-aware. Instead of hardcoding Claude Code registration, it now detects the LLM agents installed on the machine and presents an interactive checklist of which to connect to memd's MCP server.

• Interactive picker (memd setup): a dialoguer multi-select of 7 agents — Claude Code, Codex, Gemini CLI, Cursor, Windsurf, Cline, Zed — pre-checked from current state. Sync semantics: the checklist is the source of truth, so un-checking a configured agent removes memd from it. On a non-TTY (CI/piped), it auto-configures every detected agent and removes nothing.
• New src/agents/ module: a mostly-data registry. Each agent declares its detection rule, MCP registration mechanism (Claude CLI / JSON-merge / TOML-merge), an optional instruction-file for directives, and a hooks flag. All seven were verified HTTP-capable, so every agent registers the always-on daemon's HTTP endpoint (http://127.0.0.1:7702/mcp).
• memd status Agents section: reports each agent as configured (HTTP), detected — not configured, or not detected.
• Directives go to Claude Code / Codex / Gemini CLI (agents with a global instruction file); lifecycle hooks remain Claude Code only.
• Data-loss guard: memd refuses to overwrite an agent config it can't parse (JSONC configs with comments are left untouched with a warning) rather than clobbering the user's other MCP servers.

Design spec and implementation plan are in docs/superpowers/.

Test Plan

• cargo test — 54 passing (JSON/TOML merge insert/remove/idempotent/preserve/no-clobber, plan_action sync matrix, registry, directive roundtrip)
• cargo clippy --all-targets -- -D warnings — clean
• cargo fmt --check — clean
• cargo build --release — succeeds
• memd status shows the Agents section with live per-agent state
• Manually exercise the interactive MultiSelect picker on a TTY (not run in CI; verify checkbox toggles configure/remove as expected)

🤖 Generated with Claude Code