docs: load CLAUDE.md detail only where it is needed

The root file is read at every session start and had grown to 87 KB, so every
session paid for knowledge it did not use. Move the per-directory detail into
nested CLAUDE.md files, which load when a file in that directory is touched,
and the five deep-dive topics into docs/. The root keeps the commands, the hard
rules and an index of where the rest lives.

Content moved verbatim — the probed Word/LibreOffice behaviour, sentinel order
and shared constants are what the code cannot say. CI fails the root over 120
lines, since a prose budget alone is what let it grow.

.github/workflows/ci.yml

@@ -10,6 +10,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      # CLAUDE.md is read at every session start; detail belongs in the nested files.
+      - run: test "$(wc -l < CLAUDE.md)" -le 120 || { echo "CLAUDE.md over its 120-line budget"; exit 1; }
       - uses: actions/setup-node@v4
         with:
           node-version: 20