feat: add per-project worktree base directory configuration

[Maxsky5]

Closes #1830 #1620

Summary

Allow users to configure a custom directory where git worktrees are created for each project, instead of using the system temp directory (e.g., /var/folders/.../vibe-kanban-dev/worktrees).
This is useful for:

• Keeping worktrees on a specific disk/partition
• Organizing project worktrees in a predictable location (e.g., ~/my-project-worktrees)
• Avoiding temp directory cleanup issues on some systems

Changes

Database

• New migration (20260112000000_add_worktree_base_dir_to_projects.sql): Adds worktree_base_dir TEXT DEFAULT NULL column to projects table

Backend

File	Change
crates/db/src/models/project.rs	Added worktree_base_dir field to Project and UpdateProject structs, updated all SQL queries
crates/server/src/routes/projects.rs	Added path validation on project update using validate_worktree_dir()
crates/utils/src/path.rs	Added validate_worktree_dir() (checks path exists, is directory, is writable) and expand_tilde() utilities
crates/services/src/services/worktree_manager.rs	Added get_worktree_base_dir_with_config() as the single source of truth for worktree path resolution
crates/services/src/services/workspace_manager.rs	Delegates to WorktreeManager::get_worktree_base_dir_with_config()
crates/local-deployment/src/container.rs	Updated create() and ensure_container_exists() to fetch project and use its worktree_base_dir

Frontend

File	Change
frontend/src/pages/settings/ProjectSettings.tsx	Added input field for worktree base directory in General Settings card
frontend/src/i18n/locales/*/settings.json	Added translations for all 6 locales (en, es, ja, ko, zh-Hans, zh-Hant)
shared/types.ts	Regenerated TypeScript types

Bug Fix

Fixed a state management issue in ProjectSettings.tsx where the onSuccess callback from a previous render's stale closure would overwrite fresh mutation data with stale form state. The fix ensures the form state is updated from the mutation response rather than being clobbered.

Testing

• Added 6 unit tests for get_worktree_base_dir_with_config() in worktree_manager.rs:
  • None returns default worktrees path
  • Empty string returns default
  • Whitespace-only returns default
  • Absolute path is used directly
  • Tilde (~) is expanded to home directory
  • Leading/trailing whitespace is trimmed
• All existing tests pass: cargo test --workspace
• Frontend type checks pass: pnpm run check

How to Test

1. Open Project Settings for any project
2. Find "Worktree Base Directory" input in General Settings
3. Enter a valid absolute path or ~/some-path
4. Save and create a new workspace session
5. Verify the worktree is created in the specified directory

Notes

• If the field is left empty, the default temp directory behavior is preserved
• Path validation ensures the directory exists and is writable before saving
• Translations are AI-generated. Let me know if I should update any of them