Rebuild CLAUDE.md as a lean code map, archive full diary to docs/HISTORY.md

CLAUDE.md had grown from a "condensed briefing" into a ~2500-line
session-by-session bug-fix diary, expensive to load every session and no
longer doing its stated job of orienting a new session quickly. Replaced
it with a short map of where things live (code-registration pipeline,
the two background services, GUI layer) and a "known pitfall classes"
section distilling the recurring bug shapes (wx3.2/GTK3 layout
reentrancy, sizer footguns, iterator invalidation, format-string bugs)
so they're still discoverable without the full narrative.

The original content is preserved verbatim in docs/HISTORY.md, nothing
lost.

Author: andy