merge: integrate main restructuring into dev

- Resolve 57 merge conflicts from codebase restructure
- Port dev feature code to new directory structure:
  * Update import paths to use @/ aliases
  * Add backward-compatible API signatures (createInstance, startInstance, deleteInstance)
  * Add missing type exports (ProjectWithRepos, InstanceHealth, Branch, BranchesResponse)
  * Extend Session and GitRepository types for dev features
  * Extend TerminalComponent props for mobile terminal wrapper
  * Add missing icon names (bell, drag, undo)

Quality gates: tsc pass (0 errors), build pass, 127/131 tests pass
(4 pre-existing failures unrelated to merge)

AGENTS.md

@@ -90,6 +90,13 @@ Before completion, report:
 
 Do not claim completion without verification evidence.
 
+## Git branch policy
+
+- **Default working branch:** `dev` — all commits and pushes target `dev` unless the user explicitly requests otherwise.
+- `main` is the stable/production branch; merge to `main` only when explicitly instructed.
+- After committing, push to `origin/dev`.
+- If `dev` does not exist locally, create it from `main` or fetch it from origin.
+
 ## Git workflow
 
 ### Branching strategy