Root, CI, docs and packaging describe the project to a stranger (#6225)

#6225 "Comment standard sweep: root, config, CI workflows, docs and
packaging", milestone 546 "Bring the repo to the comment standard (rule 32)
and compose defaults (rule 198)".

- README restructured in newcomer order: what it is, quick start,
  configuration, setup pitfalls, updating and backups, features,
  troubleshooting, development, licence. Its quick-start compose carries
  no restart policy.
- Dockerfile and .env.example trimmed to one or two lines per setting.
- Workflows, packaging scripts and docs lose issue, run, note, rule and
  milestone references and their history narration. Comments that still
  described path filters and "step 6" as future work now state what the
  workflows do.
- ci-requirements.md rewritten against the current workflows. It said the
  build gated on typecheck and lint only, the integration lane did not
  gate, a v* tag published :latest, and ci-tauri lacked bsdtar and zstd;
  none of those is true now (the last checked against run 9630's log).
- Echo strings in guard-forward.sh and version.sh drop their note
  citations; every string a test asserts on is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/public/icon.svg

@@ -1,6 +1,6 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" role="img" aria-label="Inkwell">
   <!-- Rounded-tile app icon: brand yellow, and the inkwell — a black inkpot with a
-       quill standing in it. Source for every raster icon; see step 5 of milestone 481. -->
+       quill standing in it. Source for every raster icon. -->
   <rect width="512" height="512" rx="112" fill="#F5C518"/>
   <g transform="translate(256 256) scale(0.92) translate(-262 -226)">
   <defs>