Add structs/logging docs, wiki/07-notes with Spew architecture, fix Home index

- src/config/structs.rs: full file header + rustdoc on every struct and field
- src/logging.rs: full file header + rustdoc on init_from_config(), inline comments
- wiki/07-notes.md: design notes page — Spew/no-nazi-twitter concept documented
  (Justin Bieber fan-out problem, KWIC moderation gate, IPFS media storage,
   timeline assembly tradeoffs, open questions, architecture diagram)
- wiki/Home.md: corrected broken 07-broker-calls.md link; added notes section
- README.md: added wiki/07-notes.md to wiki index

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wiki/Home.md

@@ -20,7 +20,9 @@ If you are reading this as a new contributor, start here and read in order. The
 
 ### Messaging
 - [Queue Topology](06-queue-topology.md) — AMQP exchanges, queues, routing keys, and the broker model
-- [Broker Calls](07-broker-calls.md) — Every broker event type documented
+
+### Notes
+- [Design Notes & Discussions](07-notes.md) — Spew/no-nazi-twitter concept, open questions, architecture discussions in progress
 
 ### Data
 - [Template System](08-template-system.md) — REC and REL templates, the TLA convention, schema-as-contract