Rename release assets `ide-rules-*.zip` → `codeguard-*.zip` and simplify the update workflow

[thomas-bartlett]

The release downloads are named ide-rules-<host>.zip. That made sense
when they only contained rule files, but 5 of the 9 zips now ship skills
and subagents — the filename no longer describes what's inside.

Separately, update-codeguard-rules.yml (the workflow other repos run to
pull CodeGuard in) downloads each host's zip individually and maintains a
hand-written lookup table of directory → zip name → glob pattern. Every
new host we add means editing that table.

Phase 1 — rename:

• build-ide-bundles.yml: emit codeguard-<host>.zip (replaces
  ide-rules-<host>.zip — consumers on the old update-codeguard-rules.yml
  will need to pull the new copy).
• Update docs/getting-started.md (9 links),
  docs/claude-code-skill-plugin.md, src/formats/claude.py docstring.

Phase 2 — simplify the consumer workflow:

• update-codeguard-rules.yml: download codeguard-all.zip once,
  extract, then for each detected host dir delete codeguard-* and
  cp -R from the extracted bundle.
• Removes the FORMATS/PATTERNS maps; new host bundles get picked up
  automatically.

Relates to #64 — the rename should land before v1.4.0 is cut.

[thomas-bartlett]

One addition to Phase 1: dual-publish both codeguard-<host>.zip and ide-rules-<host>.zip for one release cycle, then drop the ide-rules-* aliases in the following release.

Repos running the current update-codeguard-rules.yml fetch ide-rules-*.zip by name — without the alias their workflow breaks silently the moment a release ships without it. One overlap release gives consumers a window to pull the updated workflow.