feat: extract in-process MCP action layer, concurrent task dispatch, and spawn/reconcile hardening

[weilinliu]

Summary

• In-process MCP action layer (artemis/mcp/action_*, actuators/): typed ActionResult, capability manifest validated at session startup, AdbActuator as the single physical implementation, in-memory ActionSession replacing the stdio-subprocess MCP in the validator (fixes the Windows spawn failure path), and McpActionExecutor preserving the legacy executor contract. adb_server keeps its external stdio/SSE surface unchanged and reuses the actuator implementation.
• Capability-gated prompt assembly (prompt_assembly.py): tool enums and teaching segments render per available backend tools; full-set output is byte-identical to the previous static text (locked by tests).
• Admin console task queue: serial worker replaced by a per-device concurrent dispatcher (ARTEMIS_CONCURRENCY_MODE=global restores serial semantics), per-session cancellation, strict device binding on enqueue, stdio piping with tee to trace stdout.log, shutdown cleanup of all active runs, and a fix for _pid_exists exception ordering (PermissionError now treated as alive).
• mcp_server reliability: spawn watchdog kills runners stuck before interpreter startup and releases device reservations; task-state reconcile uses psutil liveness, prefers runner-reported pids, and adds a 45s startup grace to stop false failure reports on Windows; conversation_id optional end-to-end; explicit device_serial validated at submission.
• CLI install: writes ~/.claude/rules/artemis.md for Claude Code and migrates/removes the legacy CLAUDE.md injection block; ~/.claude.json is never rewritten when it fails to parse.

Test plan

• Full unit suite: 895 passed, 3 skipped (Windows, project venv).
• New suites: action manifest/server/session, actuators, prompt assembly (byte-stability pins), spawn watchdog, task reconcile.