feat(agent): mount apply_patch tool for the gpt family

[TheGreatAxios]

Summary

• Implements apply_patch tool in src/agent/apply-patch-tool.ts using the existing Codex patch parser and hunk applier.
• Plans all operations (add, update, move, delete) upfront to prevent half-applied patches on hunk errors, and rejects workspace escapes.
• Mounts apply_patch across sessions and subagents while advertising it specifically for the gpt profile in place of individual file mutation tools.

Verification

• bun run typecheck, bun run build, and bun test src/agent/apply-patch-tool.test.ts pass cleanly.
• Unit tests verify add/update/delete envelope execution, atomic rollback on hunk failure, and containment enforcement.

Fixes CL-9532

[linear-code]

CL-9532