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/usage.md

@@ -0,0 +1,56 @@
+# `zappier/usage`
+
+**Package:** `zappier`  
+**Source:** `packages/zappier/src/usage.ts`  
+**Lines:** 55
+
+## What this module is
+
+Implementation module in `zappier`. The tables below are extracted from the source (signatures + JSDoc).
+
+## Exports
+
+`UsageEntry`, `UsageSummary`, `summarize`, `UsageRepo`, `InMemoryUsageRepo`
+
+## Types / interfaces / classes
+
+| Kind | Name |
+|------|------|
+| interface | `UsageEntry` |
+| interface | `UsageSummary` |
+| interface | `UsageRepo` |
+| class | `InMemoryUsageRepo` |
+
+## Functions
+
+| Name | Parameters | Param types (JSDoc) | Returns | Calls (same file / helpers) |
+|------|------------|---------------------|---------|-----------------------------|
+| `summarize` | `customerId: string, list: UsageEntry[]` | — | `unknown` | see Call graph |
+
+## Methods (class / object)
+
+| Name | Parameters |
+|------|------------|
+| `record` | `entry: UsageEntry` |
+| `listFor` | `customerId: string, since?: Date` |
+| `summaryFor` | `customerId: string, since?: Date` |
+| `record` | `entry: UsageEntry` |
+| `listFor` | `customerId: string, since?: Date` |
+| `summaryFor` | `customerId: string, since?: Date` |
+
+## What it imports / requires
+
+_No imports detected._
+
+## Call graph (identifiers invoked)
+
+`summarize`, `reduce`, `record`, `listFor`, `summaryFor`, `push`, `filter`
+
+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`.
+