UX: module completion screen with forward look and resources

Part of the UX backlog. Raised on 2026-06-11 as three related items: celebratory moments, a forward look, and resources on the completion screen.

Finishing a module currently just marks it complete. There is no payoff, and no signposting to what comes next.

Scope

When a module is completed:

• acknowledge it visibly — a celebratory moment, not just a state change
• show the forward look for that module
• show its resources / official docs links

Both of the latter already exist as data: the manifest carries official_docs, reuses_existing and spiral_refs, and the markdown files have a "Forward look" section that lib/content.ts already knows how to find (extract_forward_look logic existed in the old build script; check what content.ts currently exposes).

Related but separate

The "Congratulations page at the end of the beginner track" is a content task, tracked separately — this issue is the per-module completion experience.

Where

components/ModulePlayerClient.tsx, lib/content.ts, lib/manifest.ts.

Done when

Completing a module shows a completion state with its forward look and resources, sourced from existing manifest/markdown data rather than hardcoded.

Start in components/ModulePlayerClient.tsx to trace the module completion flow, then inspect lib/content.ts for the extract_forward_look logic and lib/manifest.ts for official_docs, reuses_existing, and spiral_refs. Done means the completion state visibly acknowledges completion and displays the module's forward look and resources from the existing manifest and markdown data.