feat: add workspace project lifecycle teardown

[neversettle17-101]

Summary

• extend the workspace project adapter port with per-repo destroy, force-destroy, restore, preserve, and apply operations
• route kill, cleanup, shutdown, reconcile, and restore-all through session_worktrees for workspace projects
• preserve dirty workspace-project repos before force-removal, mark successful interactive removals non-restorable, and mark failed removals retry_remove
• move stray restore paths aside before recreating workspace-project worktrees

Scope

This is the next backend milestone after workspace-aware spawn in #2224: multi-worktree kill/cleanup/shutdown/restore using session_worktrees rows. It does not include frontend work, workspace-aware SCM observation, root land/discard APIs, or full workspace status aggregation.

Tests

• cd backend && go test ./internal/session_manager
• cd backend && go test ./internal/adapters/workspace/gitworktree
• cd backend && go test ./internal/storage/sqlite/store -run 'TestSessionWorktreesRoundTrip|TestUpsertSessionWorktreeEmptyStateDefaultsToActive'\n\nPart of Complete backend support for workspace projects #2222.