#9782: feat(hooks): implement session:start and session:end lifecycle events

## Summary Implements the session lifecycle hooks that were previously listed as "Future Events" in the docs. Supersedes #3804 (which was closed due to test failures). ### Changes - **session:end**: Triggered BEFORE `/new` or `/reset` clears the session - Context: `sessionEntry` (previous session), `sessionId`, `sessionFile`, `reason` (`"new"` or `"reset"`), etc. - **session:start**: Triggered when a new session begins (after reset/new) - Context: `sessionEntry`, `sessionId`, `sessionFile`, `isReset` (`true` for `/reset`, `false` for `/new`), etc. ### Event Order For `/new` or `/reset` commands: 1. `session:end` (if previous session exists) 2. `command:new` or `command:reset` 3. `session:start` (if new session exists) ### Use Cases - Save session context/transcripts to external memory systems on session end - Initialize session-specific resources on session start - Audit session lifecycle events - Trigger cleanup or archival workflows when sessions reset ### Docs Updated `hooks.md` to move session events from "Future Events" to a new "Session Events" section with full documentation. ### Testing Added tests covering: - session:end fires before command:new when previous session exists - session:start fires with isReset context - session:end does not fire when no previous session exists <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds two new internal hook events to the command pipeline for `/new` and `/reset`: - Emits `session:end` before triggering `command:new|command:reset` so hooks can persist the prior session before it is cleared. - Emits `session:start` after the command hook so hooks can initialize resources for the new session. - Updates `docs/hooks.md` to document these new session lifecycle events and adds tests validating call order and presence/absence. The implementation lives in `src/auto-reply/reply/commands-core.ts`, which is where command hooks are currently created and dispatched via `createInternalHookEvent(...)` / `triggerInternalHook(...)`. <h3>Confidence Score: 4/5</h3> - Mostly safe to merge, but the new session hook context fields are currently inaccurate for `/new` vs `/reset`. - Change is localized and covered by tests, but `session:start` always sets `isReset: true` and `session:end` always uses `reason: "reset"`, which will mislead hook consumers and is likely to break intended behavior once hooks depend on these fields. - src/auto-reply/reply/commands-core.ts <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->