feat: bulk validator tab + status/niche/type browse filters

- New app/validator.py: background HTTP checker for entire dataset
  - 50 concurrent checks, skips already-validated domains
  - Extracts prescreen_status, server, IP, load_time_ms
  - start/stop/status API at /api/validator/start|stop|status

- New dedicated "Validator 🔬" tab with stats grid, TLD filter,
  Start/Stop controls, live progress indicator

- Browse tab: "Live" column replaced with "Status" dot (color-coded
  ● from prescreen_status, falls back to is_live)
- Browse tab: new Status / Niche / Type filter dropdowns

- db.py: added ip TEXT + load_time_ms INTEGER columns + migrations;
  get_enriched() supports prescreen_status/niche/site_type filters

- main.py: /api/enriched extended with prescreen_status/niche/site_type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/db.py

@@ -40,7 +40,9 @@ CREATE TABLE IF NOT EXISTS enriched_domains (
     prescreen_status TEXT,
     niche TEXT,
     site_type TEXT,
-    prescreen_at TEXT
+    prescreen_at TEXT,
+    ip TEXT,
+    load_time_ms INTEGER
 );
 CREATE TABLE IF NOT EXISTS job_queue (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -84,6 +86,8 @@ _MIGRATIONS = [
     "ALTER TABLE enriched_domains ADD COLUMN niche TEXT",
     "ALTER TABLE enriched_domains ADD COLUMN site_type TEXT",
     "ALTER TABLE enriched_domains ADD COLUMN prescreen_at TEXT",
+    "ALTER TABLE enriched_domains ADD COLUMN ip TEXT",
+    "ALTER TABLE enriched_domains ADD COLUMN load_time_ms INTEGER",
 ]
 
 # Index build state
@@ -315,7 +319,9 @@ async def get_stats():
 # ── Enrichment helpers ───────────────────────────────────────────────────────
 
 async def get_enriched(min_score=0, cms=None, country=None, kit_digital=None,
-                        ai_only=False, lead_quality=None, page=1, limit=100):
+                        ai_only=False, lead_quality=None,
+                        prescreen_status=None, niche=None, site_type=None,
+                        page=1, limit=100):
     offset = (page - 1) * limit
     conditions = ["score >= ?"]
     params: list = [min_score]
@@ -333,6 +339,17 @@ async def get_enriched(min_score=0, cms=None, country=None, kit_digital=None,
     if lead_quality:
         conditions.append("ai_lead_quality = ?")
         params.append(lead_quality.upper())
+    if prescreen_status == "none":
+        conditions.append("prescreen_status IS NULL")
+    elif prescreen_status:
+        conditions.append("prescreen_status = ?")
+        params.append(prescreen_status)
+    if niche:
+        conditions.append("niche = ?")
+        params.append(niche)
+    if site_type:
+        conditions.append("site_type = ?")
+        params.append(site_type)
     where = "WHERE " + " AND ".join(conditions)
     async with aiosqlite.connect(SQLITE_PATH) as db:
         db.row_factory = aiosqlite.Row