Engine Phase 4: curate robustness + calibration + seniority inference

The measurement showed the USER-FACING Opus score is already well-calibrated — the real bug was curate
FAILING and dropping to the bad white-box fallback:
- curate.py: _salvage_kept() brace-scans + parses each kept object independently, so one bad char or a
  max-tokens truncation no longer drops the whole shortlist. max_tokens 4000 → 8000 (28 sifted jobs ×
  full report cards overflowed). This fixed the sales case (was failing → fallback).
- curate.py: calibration nudge in the prompt — a genuinely strong current-state match is a real low-80s,
  partial/stretch 60s-70s; don't under-sell strong matches into the 60s (without inflating weak ones).
- normalize.py + search.py: _seniority_from_title() infers seniority from the title (conservative) when a
  board omits it, applied centrally in the sweep → the experience factor + Opus brief aren't blind.

Verified (live Opus on the regression cases): tech MAE 9.8→4.5, sales FAILED→MAE 5.3 (kept 13),
ops 4.2→3.3 — user-facing scores now MAE 3-5 with zero curate failures. 31 tests pass.

app/engine/normalize.py

@@ -106,6 +106,25 @@ def _salary_from_amount(amount: int | None, per_year: bool) -> tuple[float | Non
     return lpa, f"₹{lpa:g}L/yr"
 
 
+_TITLE_SENIORITY = [
+    (r"\b(intern|trainee|fresher|graduate|entry[- ]?level|jr|junior)\b", "junior"),
+    (r"\b(associate)\b", "mid"),
+    (r"\b(senior|sr|staff|manager|specialist)\b", "senior"),
+    (r"\b(lead|principal|head|director|vp|chief|cxo|founding)\b", "lead"),
+]
+
+
+def _seniority_from_title(title: str | None):
+    """Infer seniority from a job title when the board omits it — so the experience factor + Opus brief
+    aren't blind. Conservative: only clear signal words; ambiguous titles stay None."""
+    t = (title or "").lower()
+    hit = None
+    for pat, sen in _TITLE_SENIORITY:   # last match wins → "Lead"/"Director" beats "Senior"
+        if re.search(pat, t):
+            hit = sen
+    return hit
+
+
 def _seniority_from_years(min_yrs: int | None):
     if min_yrs is None:
         return None