Add saved filter views and redesign findings dashboard

[khat190]

What Changed

Frontend

• frontend/src/hooks/useSavedViews.ts — new custom hook managing full preset CRUD. Writes to localStorage immediately (offline-safe) and syncs to the backend when reachable. Validates every preset on read so corrupt/malformed data is silently discarded rather than crashing the UI.
• frontend/src/components/SavedViewsPanel.tsx — new dropdown panel component placed in the Findings filter row. Supports: save current filters under a named preset, apply a saved preset in one click, inline rename (click edit icon → type → blur/Enter commits), two-click delete (confirm guard), and animated feedback on save/error.
• frontend/src/pages/Findings.tsx — minimal diff from original. Added useSavedViews() hook, currentPreset snapshot, applyPreset() restore function, and <SavedViewsPanel> in the sort-pills row. All existing filter logic, finding rows, and detail panel are untouched.

Backend

• backend/secuscan/saved_views.py — new self-contained FastAPI router registered at /api/v1/saved-views. Full CRUD: GET (list), POST (create, 409 on duplicate name), PUT (overwrite/rename), DELETE (idempotent). FilterPreset is a Pydantic model with field validators on sortMode and severity so invalid values are rejected at the boundary with 422.
• backend/secuscan/main.py — two lines added: import saved_views_router and app.include_router(saved_views_router).

Database

The saved_views table is created via CREATE TABLE IF NOT EXISTS on first request (idempotent). No migration script needed; no existing tables are modified.

Why It Changed

Power users repeatedly configure the same filter combinations (e.g. critical severity + specific target + last 7 days) and had no way to persist them. This feature adds a named-preset system that survives page reloads and browser restarts, with optional backend persistence for multi-session durability.

API Surface

Method	Path	Behaviour
GET	/api/v1/saved-views	List all saved views
POST	/api/v1/saved-views	Create (409 if name exists)
PUT	/api/v1/saved-views/{id}	Overwrite preset and/or rename
DELETE	/api/v1/saved-views/{id}	Delete (idempotent, always 200)

How to Test
Backend tests

pytest testing/backend/unit/test_saved_views.py -v

22 tests covering: create, list, apply (round-trip), overwrite, rename, delete, duplicate name (409), invalid JSON (422), invalid enum values (422), empty name (422), name-too-long (422), non-existent ID (404), idempotent delete, and partial update.

Frontend tests

npx vitest run frontend/testing/unit/hooks/useSavedViews.test.ts

20 tests covering: create, localStorage persistence, apply/restore, overwrite (same name), case-insensitive overwrite, rename, rename-to-empty throws, delete, idempotent delete, invalid preset throws, corrupt localStorage recovery, mixed valid/invalid data on mount, multiple independent views.

Trade-offs & Known Limitations

• No auth: saved views are per-browser (localStorage) or per-server (no user concept in the current backend). This matches the existing SecuScan local-first model.
• Backend sync is optimistic: if the backend is unreachable, saves go to localStorage only; they sync on the next successful request. No retry queue.
• Name uniqueness is case-insensitive on the backend (SQL LOWER()) but case-preserving on display, consistent with how the workflows endpoint behaves.

Screenshots

CLoses: #235