Document LmxProxy protocol in DCL, strengthen plan generation traceability guards, and add UI constraints

- Replace "custom protocol" placeholder with full LmxProxy details (gRPC transport, SDK API mapping, session management, keep-alive, TLS, batch ops)
- Add bullet-level requirement traceability, design constraint traceability (52 KDD + 6 CD), split-section tracking, and post-generation orphan check to plan framework
- Resolve Q9 (LmxProxy), Q11 (REST test server), Q13 (solo dev), Q14 (self-test), Q15 (Machine Data DB out of scope)
- Set Central UI constraints: Blazor Server + Bootstrap only, no heavy frameworks, custom components, clean corporate design

HighLevelReqs.md

@@ -54,7 +54,7 @@
 - Store-and-forward buffers are persisted to a **local SQLite database on each node** and replicated between nodes via application-level replication (see 1.3).
 
 ### 2.4 Data Connection Protocols
-- The system supports **OPC UA** and a **custom protocol**.
+- The system supports **OPC UA** and **LmxProxy** (a gRPC-based custom protocol with an existing client SDK).
 - Both protocols implement a **common interface** supporting: connect, subscribe to tag paths, receive value updates, and write values.
 - Additional protocols can be added by implementing the common interface.
 - The Data Connection Layer is a **clean data pipe** — it publishes tag value updates to Instance Actors but performs no evaluation of triggers or alarm conditions.