Add Pi process-local Autopilot execution

[drafael]

Summary

• package an Autopilot Pi extension that invokes the coordinator core in the owning Pi process
• delegate implementation attempts through the public structured pi-subagents event API with exact request/run/node/subject/harness-instance fencing
• retain the direct Pi CLI path as an explicit fallback and as the runtime-owned independent-review path
• fail closed on admission loss, terminal-response loss, idle/deadline expiry, session shutdown, reload, and harness replacement
• export signal-free coordinator entry points while preserving CLI-only signal ownership
• retire the old outer-Pi slash-command bridge and update operator/recovery documentation

Safety properties

• ATTEMPT_STARTED is durable before delegation
• ATTEMPT_EXECUTION_ADMITTED records the exact captured execution subject
• loss before subject capture or after admission becomes EXECUTION_STATE_UNKNOWN; no replacement is launched
• only the coordinator writes lifecycle state
• cancellation and terminal results require the exact delegation tuple
• worker output and activity are bounded and credential-redacted
• cooperative completion does not claim OS process-tree quiescence

Validation

• npm run typecheck
• npm run lint
• npm run format:check
• npm test — 200 tests, 192 passed, 8 platform skips, 0 failed
• generated dist rebuilt and checked
• changed Markdown links checked
• git diff --check
• package dry-run contains the Pi extension and in-process adapter, with no .exe or .node
• live Pi 0.84.4 + pi-subagents 0.60.0 normal completion in one reused local repository: SUCCEEDED
• live whole-process loss in the same local repository: resumed as WAITING/execution-unknown with exactly one attempt; operator stop recovery succeeded
• live pause during a shell tool call: exact cancellation, zero charged attempts, WAITING/operator-pause
• independent correctness/security re-review: no issues found

No GitHub or GitLab validation repositories were created.