docs: split CLAUDE.md deep detail into architecture-invariants, ignore it in prettier

CLAUDE.md was 110KB (~27.5k tokens) loaded into every session, with 30 lines
carrying 49% of the bytes as single-paragraph walls (the Docker cases entry
alone was 9,388 chars). Extract the implementation detail verbatim into
docs/architecture-invariants.md (41 sections) and leave the rule plus a
pointer inline. Result: 59.5KB, ~14.9k tokens, 46% smaller.

Also:

- Add CLAUDE.md to .prettierignore. Prettier's markdown printer escapes
  underscores in the glob-heavy paths used throughout, which had already
  corrupted the Ultracode paragraph (agent-*.jsonl became agent-\_.jsonl,
  collapsing backtick spans). npm run format:check is unaffected; its globs
  are src/** only.
- Move version archaeology (PR numbers, ticket ids, commit shas, "was X now
  Y" lineage) into the invariants doc, keeping the rules and their reasoning
  inline.
- De-duplicate the Core Files table against Key Patterns.
- Document install.sh in Scripts, and why Prettier's scope is deliberately
  narrow (14 hand-formatted public JS modules are guarded by
  check:public-assets and check:frontend-syntax instead).

Two factual fixes found while verifying: displayKeys is a client-side merge
policy, not a wire filter, and showResponseViewer / showPlanUsageLimits /
language are declared in SettingsUpdateSchema and do persist server-side; and
the respawn route count is 7, not 18.

Verified: 30/30 cross-doc pointers resolve, 1,184 of 1,190 backticked
identifiers from the original survive (the 6 others are dropped archaeology
or the prettier-corrupted spellings), 59 table rows well-formed,
format:check and check:frontend-syntax clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: claude

.prettierignore

@@ -26,3 +26,6 @@ src/web/public/terminal-ui.js
 src/web/public/voice-input.js
 src/web/public/upload.html
 scripts/remotion/
+
+# Hand-maintained; Prettier escapes underscores in glob paths and corrupts paragraphs.
+CLAUDE.md