docs: make tutorials self-contained and document the current core API

[ravenSanstete]

Core tutorials previously linked runnable files without showing their implementation, and the API reference omitted the current Session/composition surface. Developers can now build the synthetic notes Agent using complete files on each EN/zh page, follow its lifecycle and extension lessons, and navigate to source-checked API signatures.

• Adds a single notes project with independent chapters, explicit fake providers, real Session/tools/persistence, deterministic parallel ordering, Docker artifacts/publication, child execution and serialized handoff.
• Splits navigation into getting started, learning, task guides and API reference. Keeps earlier API text explicitly historical and preserves existing entry URLs.
• Adds source-to-MDX checks, a public-symbol inventory and installed-wheel execution of the files extracted from the webpages; ordinary docs CI never sends model requests.

Validation: 787 passed / 1 Docker opt-in skip across the targeted suites; separate Docker-page/golden-path/scaffold/smoke qualification 17 passed. 166 MDX pages compile, and 46 changed routes rendered successfully at desktop and mobile widths. Clipboard and symbol-anchor navigation passed. Runtime, package metadata and quality allowances are unchanged.

Known boundary: concurrent same-Session handoff destination restore and source completion callbacks can conflict on owner CAS at the frozen runtime. The runnable example explicitly serializes transfer acknowledgement, source cleanup and destination execution, verifies actual destination execution, and records the unsupported concurrent case without changing the kernel.

Runtime identity: 60809b3. Historical G5 qualification remains bound to 717b4cf. See docs/internal/plans/docs_self_contained_qualification.md for source-bound local evidence. Live Mintlify publication is verified separately after merge.