chore: prepare yanting monorepo handoff

report-notebooklm-api/docs/SOURCE_INDEX.md

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+# Source Index
+
+This is a handoff snapshot, not the product SSOT.
+
+Product SSOT: mall-docs report-notebooklm docs, snapshot date: 2026-06-03.
+
+## Snapshot Sources
+
+The handoff documents in this repository were distilled from these logical product-document sources:
+
+| Logical source | Used for |
+|---|---|
+| `phase1-scope.md` | Product positioning, target users, tabs, Phase 1 scope, non-goals, compliance boundary, Vision decoupling. |
+| `phase1-build-brief.md` | Data tables, endpoint list, display module model, artifact enum, seed mapping, open questions. |
+| `phase1-development-plan.md` | Technology choices, architecture, Redis/object-storage strategy, phases, deployment assumptions, external dependencies. |
+| `data-model-api-contract-v0.1.md` | API/data object intent and response boundaries. |
+| `user-flows.md` | Guest vs logged-in behavior, shallow interaction expectations, no-download clarification. |
+| `app-prd-v0.1.md` | App-side behavior and page-level expectations. |
+| `vision-research-sources.md` | Source-reference context and Vision decoupling principle. |
+
+## Drift Rule
+
+Do not treat this repository snapshot as the product SSOT. When product requirements change:
+
+1. Update the product SSOT first.
+2. Update this code-repo snapshot only for information needed by engineers.
+3. Bump the snapshot date or add a short changelog entry.
+
+## What Was Not Copied
+
+- Historical drafts.
+- Full experiment reports.
+- Local-only evidence paths.
+- Private local notes.
+- Raw NotebookLM notebook IDs, source IDs, conversation IDs, account identifiers, or payloads.