feat(learning): Day-0 onboarding deck, streaming Feynman simulator, cross-tool loops & architecture linter

[arvarik]

Summary of PR 2

1. Day-0 Onboarding & Curated Starter Decks:

   • Added a curated starter deck (System Design Foundations) with 15 high-yield architecture flashcards covering Consistent Hashing, CAP Theorem, Database Indexing (B-Tree vs LSM), Load Balancing (L4 vs L7), Cache-Aside, Token Bucket Rate Limiting, Sharding, Message Queues vs Event Streams, Circuit Breakers, CDNs, Bloom Filters, Two-Phase Commit, Write-Ahead Logs, Gossip Protocols, and Quorums.
   • Every card has tags/concept keywords matching the Knowledge Graph prerequisite map, instantly populating SM-2 memory health.
   • Enhanced BlueprintShell to synthesize curriculum context for empty topics so cards can be generated on Day 0 before manual notes are written.

2. Streaming Feynman Technique Simulator:

   • Enabled token-by-token real-time streaming Markdown in FeynmanPage with abort controller and a dedicated Stop button.
   • Added cross-tool action shortcuts: 'Practice Gaps in Chat' (prefills chat draft with missing points), 'Study Flashcards', and 'New Topic'.

3. Cross-Tool Learning Loops:

   • In FlashcardView: Added cross-tool action bar to jump directly into the corresponding Guide Blueprint note, launch the Architecture Canvas, or ask the AI Tutor with prefilled concept context.
   • In ExportMenu: Added 'Export to Canvas' action that converts calculated Back-of-the-Envelope capacity estimates directly into whiteboard observability nodes.

4. Whiteboard Architecture Linter:

   • Implemented architectureLinter.js detecting single points of failure (SPOF), direct client ingress without gateway/LB, unbuffered writes, uncached reads, orphan nodes, and missing rate limiters.
   • Added ArchitectureAuditModal with score metrics, severity-ranked findings, and best practice badges.
   • Added an interactive 'Audit' button in the builder toolbar.

Verification

• npm run lint passed (0 errors, 0 warnings).
• npm test passed (20 test suites, 261 passed, 2 skipped).
• npm run build passed.