Smoother search in Edit Role and Vendor file views, plus shared-constant cleanup

Fixes two search boxes that fired a request on every keystroke — permission search in the Admin Edit Role dialog and file search in the Vendor View Files modal — so they now wait until typing pauses (300ms). It also consolidates two shared configuration values into a single source of truth used by all frontend apps. This change has reached the QA environment.

Both search inputs were sending traffic on every character typed: the Edit Role permission search triggered an API call per keystroke, and the Vendor View Files search pushed a WebSocket query per keystroke. That generated unnecessary backend/socket load and could surface partial or out-of-order results while a user was still typing. Separately, the same two settings (search debounce delay and text-truncation length) were duplicated in three apps, which is easy to let drift out of sync.

Searching permissions in the Admin Edit Role dialog and searching files in the Vendor View Files modal now feels steadier: results refresh once after typing stops rather than flickering with each letter, and far fewer redundant requests are sent. No visible behavior changes elsewhere — the constants cleanup is internal and preserves the existing 300ms delay and 50-character truncation values.

• Admin Edit Role dialog (RoleFormDialog/index.tsx): wraps the available/assigned permission search terms in the existing useDebounce hook (300ms) before passing them to useRoleDetail; when a search box is cleared it bypasses the debounce so a stale filter isn't re-sent if the dialog is quickly reopened.
• Vendor View Files modal (ViewFilesModal.tsx): debounces searchQuery and uses the debounced value in both get_files WebSocket requests, with effect dependencies updated accordingly.
• Shared constants: adds packages/ui/src/constants/app.constants.ts defining GLOBAL_DEBOUNCE_DELAY_MS (300) and MAX_TRUNCATED_CHARS_TO_SHOW (50), exported via a new @dsm/ui/constants entry in the package.
• Deletes the duplicate app.constants.ts from the admin, vendor, and mail apps and repoints all imports (1 file in admin, 3 in vendor, 33 in mail) to @dsm/ui/constants. Values are unchanged.
• Net diff is small (~77 additions / 60 deletions); most changed files are one-line import swaps.

Low. The bug fixes touch only two components and reuse an existing, proven debounce hook. The main risk is the broad import-path change (37 files) — a missed or mistyped import would break a build — but the constant values themselves are identical, so runtime behavior is preserved. Mitigation: confirm all three apps (admin, vendor, mail) build cleanly and that the new @dsm/ui/constants export resolves.

• Admin > Edit Role: type in the available and assigned permission search boxes and confirm the API call fires only after typing stops (~300ms), not per keystroke; clear the search, reopen the dialog quickly, and confirm the prior filter is not re-applied.
• Vendor > View Files modal: type in the file search and confirm WebSocket get_files messages are sent only after typing pauses; verify results still match the search term and pagination/date filter still work.
• Build/smoke: verify admin, vendor, and mail apps build and load without import errors; spot-check truncated text still cuts at 50 characters and other debounced search/filter inputs across mail (grids, async selects) behave as before.