refactor(session): route reaper through typed teardown

[ElbertePlinio]

Summary

• compose opportunistic reaping through desktop, Android, and browser typed teardown owners
• keep registry iteration, liveness, retry metadata, and failed evidence finalization in core
• remove the duplicate core PID/profile teardown path and preserve retry/confinement contracts
• refuse Android serial signaling when the recorded emulator PID is already dead

Validation

• bun run test packages/core/test packages/desktop-linux/test packages/android/test packages/browser/test packages/cli/test/browser-session.test.ts packages/cli/test/commands.test.ts packages/cli/test/session-status.test.ts packages/cli/test/watch.test.ts packages/mcp-server/test/android.test.ts packages/mcp-server/test/browser.test.ts packages/mcp-server/test/desktop.test.ts packages/mcp-server/test/session-status.test.ts packages/mcp-server/test/tools.test.ts (644 passed, 2 skipped)
• focused post-review fix validation: 47 passed
• bun run typecheck
• bun run build

Refs #44 (CAND-2)