Add zero-revenue 499-A filing at $179

New service slug fcc-499a-zero for carriers with no telecom revenue:
- $179 instead of $499 (no revenue analysis needed)
- Minimal intake: entity, officer, filer ID, filing type only
- Skips revenue schedules (blocks 3-4), USF calculations (block 5),
  traffic study upload, and revenue workbook generation
- Fills blocks 1-2 and 6 only, all revenue lines left as zero

Compliance checker: shows both options (mutually exclusive checkboxes)
Order page: maps form_499a_zero to fcc-499a-zero slug
Handler: detects slug and skips revenue pipeline
DC Agent shown when either 499-A variant is checked

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/workers/services/__init__.py

@@ -61,6 +61,7 @@ SERVICE_HANDLERS: dict[str, type] = {
     "rmd-filing": RMDFilingHandler,
     "cpni-certification": CPNIFilingHandler,
     "fcc-499a": Form499AHandler,
+    "fcc-499a-zero": Form499AHandler,  # same handler, zero_revenue flag set from slug
     "fcc-499a-499q": Form499ABundleHandler,
     "stir-shaken": StirShakenHandler,
     # BDC triple — same handler, mode auto-resolved from slug
@@ -96,6 +97,7 @@ FCC_SERVICE_SLUGS: frozenset[str] = frozenset({
     "rmd-filing",
     "cpni-certification",
     "fcc-499a",
+    "fcc-499a-zero",
     "fcc-499a-499q",
     "stir-shaken",
     "bdc-filing",