feat(sync): sync_phase_failures table for escalation tracking

New table sync_phase_failures(run_id, phase, error_summary, created_at)
with index on (phase, created_at). Minimal schema — no raw payload, no
PII — stores just enough to answer "did phase X fail in the last N
runs?" for the escalation check and the /api/sync/health pill.

Helpers in sqlite_service:
  record_phase_failure(run_id, phase, error_summary)
    INSERT OR REPLACE semantics (one row per run+phase), then prunes
    to the most recent 100 sync_runs. error_summary clipped at 500
    chars defensively.
  get_recent_phase_failures(limit=3) → {phase: count} across the last N
    runs, ordered by started_at desc.

6 unit tests cover creation, counting, pruning, empty state,
idempotency, and limit semantics.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/database.py

@@ -186,6 +186,15 @@ CREATE TABLE IF NOT EXISTS anaf_cache (
     denumire_anaf TEXT,
     checked_at    TEXT NOT NULL
 );
+
+CREATE TABLE IF NOT EXISTS sync_phase_failures (
+    run_id         TEXT NOT NULL REFERENCES sync_runs(run_id),
+    phase          TEXT NOT NULL,
+    error_summary  TEXT,
+    created_at     TEXT DEFAULT (datetime('now')),
+    PRIMARY KEY (run_id, phase)
+);
+CREATE INDEX IF NOT EXISTS idx_spf_phase_time ON sync_phase_failures(phase, created_at);
 """
 
 _sqlite_db_path = None