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/models/Customer.md

@@ -0,0 +1,27 @@
+# Customer
+
+**Kind:** interface  
+**Defined in:** `packages/zappier/src/auth.ts`
+
+## Fields
+
+| Field | Type | Meaning |
+|-------|------|---------|
+| `id` | `string` | cust_… |
+| `name` | `string` | Display |
+| `tierId` | `string` | Matches TierConfig.id |
+| `apiKey` | `string` | x-api-key value |
+| `multiplierOverride` | `number?` | Beats tier multiplier |
+| `email` | `string?` | Portal login |
+
+## Who constructs it
+
+CustomerRepo.findByApiKey / findById
+
+## Who consumes it
+
+`apiKeyAuth`, `portal`, `invoices`, `usage.summaryFor`
+
+## Related modules
+
+See `docs/modules/` for the functions that take these types as parameters and the values they return.