docs: split CLAUDE.md into root, src/web/CLAUDE.md and docs/releasing.md

The root CLAUDE.md had grown to 202 KB, all of it loaded into every
session. This lands the split drafted on 2026-10-10 (it sat uncommitted
in the shared checkout through two releases), redone on top of today's
master so nothing that landed since is lost:

- src/web/CLAUDE.md: the frontend invariants (every src/web/public/ UI
  subsystem, the module notes, the XLSX preview limits, the z-index
  stack). Claude Code loads it when a file under src/web/ is read; the
  root file tells sessions to Read it before editing src/web/public/.
  Its link targets are relative to the file so they resolve on GitHub.
- docs/releasing.md: the COM procedure (now nine steps, with the MCP
  registry publish), behind a pointer in the root COM section. The
  Version line stays in the root file.
- Root CLAUDE.md (130 KB): everything else, plus the split's trims: the
  Core Files table, the reference-only rows of the Additional Commands
  table, Data Flow and the respawn presets, whose rules already live in
  the root's other paragraphs (the "Read before touching a subsystem"
  line keeps the table's doc pointers).

Every other paragraph of master's CLAUDE.md lands in exactly one of the
three files, checked line by line; the paragraphs master changed since
the draft (tile grid, OSC 52, prompt uploads, file-path links and the
HTML view, markdown preview, z-index, MCP server, agent CLI and others)
are in their current form. Both new files join CLAUDE.md in
.prettierignore. Four code comments and docs/architecture-invariants.md
now point at src/web/CLAUDE.md for the moved sections.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -2,7 +2,7 @@
 
 Implementation detail extracted from `CLAUDE.md` so that file stays small enough to load into every session cheaply. Most sections are the original paragraphs, verbatim, including the version history and PR references that explain *why* each rule exists; newer ones are written here first and summarized back into `CLAUDE.md` as a short rule plus a pointer.
 
-`CLAUDE.md` keeps the short form of each rule plus a pointer to the section here. Read the pointer first; come here when you need the mechanism, the file names, or the history behind a constraint.
+`CLAUDE.md` keeps the short form of each rule plus a pointer to the section here; for the frontend (`src/web/public/`) that short form lives in `src/web/CLAUDE.md`, which the root file points to. Read the pointer first; come here when you need the mechanism, the file names, or the history behind a constraint.
 
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