feat(coder): add hashline editing core + wire audit hooks into dispatch pipeline
Hashline editing: content-hash anchors for edit_file stale-patch detection.
Pure-JS xxHash32, line hash computation, validation with HashlineMismatchError,
256-entry hash dictionary. 6 files in apps/coder/src/services/hashline/.
Audit hooks: emitHook('tool.execute.after') wired in frame-emitter.ts for
completed/failed tool results. emitHook('turn.end') wired at terminal points
in dispatcher.ts (all 5 run functions: native, external, opencode, warm ACP,
claude SDK). Fire-and-forget, non-blocking.