Milestone 2: module/model docs (MD, Sphinx RST, PDF) and work log

74 source modules documented with extracted signatures, JSDoc params,
imports, and call graphs. 10 first-class models (PriceRule through
StatusResponse) have their own MD/RST/PDF. Sphinx HTML builds from
docs/sphinx. Per-module PDFs in docs/modules-pdf and docs/models-pdf.

Middleware gates 2–6 and 10 pass on MOCK_VERAE without NATS.

Learned: RST includes are relative to the RST file; keep one PDF per
module; Add Numbers remains the only push required tomorrow.

docs/sphinx/modules/zappier/db/billing-repo.md

@@ -0,0 +1,57 @@
+# `zappier/db/billing-repo`
+
+**Package:** `zappier`  
+**Source:** `packages/zappier/src/db/billing-repo.ts`  
+**Lines:** 69
+
+## What this module is
+
+Implementation module in `zappier`. The tables below are extracted from the source (signatures + JSDoc).
+
+## Exports
+
+`BillingReportRepo`, `JobLockRepo`, `SqliteBillingReportRepo`
+
+## Types / interfaces / classes
+
+| Kind | Name |
+|------|------|
+| interface | `BillingReportRepo` |
+| interface | `JobLockRepo` |
+| class | `SqliteBillingReportRepo` |
+
+## Functions
+
+_No top-level functions extracted._
+
+## Methods (class / object)
+
+| Name | Parameters |
+|------|------------|
+| `getReportedCents` | `customerId: string, period: string` |
+| `upsertReportedCents` | `customerId: string, period: string, cumulativeCents: number` |
+| `tryAcquireLock` | `name: string, ttlMs: number` |
+| `releaseLock` | `name: string` |
+| `constructor` | `private db: Database.Database,
+    private now: (` |
+| `getReportedCents` | `customerId: string, period: string` |
+| `upsertReportedCents` | `customerId: string, period: string, cumulativeCents: number` |
+| `tryAcquireLock` | `name: string, ttlMs: number` |
+| `releaseLock` | `name: string` |
+
+## What it imports / requires
+
+- `better-sqlite3`
+
+## Call graph (identifiers invoked)
+
+`getReportedCents`, `upsertReportedCents`, `tryAcquireLock`, `releaseLock`, `constructor`, `exec`, `billing_reports`, `job_locks`, `prepare`, `get`, `run`, `now`
+
+Each identifier is a call site in this file. Follow the import list to see the defining module; open that module’s MD for parameter and return types.
+
+## Return values (how to read this)
+
+- HTTP route handlers return Express `res.json(...)` bodies (see route docs).
+- Zapier `perform` functions return a **single object** (creates) or an **array** (triggers/searches).
+- Pricing functions return integer **cents** on `Quote.totalCents`.
+