docs(packaging): document forking/renaming the bundle identifier

[dbgeek]

What

Adds a "Forking / renaming the bundle identifier" section to docs/packaging.md, between "Why a stable signing identity" and the signing-identity setup.

Why

me.ba78.type-wave is the maintainer's domain-derived (ba78.me → me.ba78) reverse-DNS bundle id, and the docs previously presented it as a fixed given — a cloner had no guidance on whether they need their own, or which files to touch. The section:

• States that keeping it for a local build is harmless (internally-consistent string; each build is signed with the builder's own `type-wave dev` cert, so its Designated Requirement never collides with anyone else's install).
• Lists every load-bearing site to change when forking to distribute:
  • `packaging/install.sh` — `BUNDLE_ID` + `LABEL`
  • `packaging/Info.plist` — `CFBundleIdentifier`
  • `packaging/me.ba78.type-wave.plist` — the `Label` value and the filename (`install.sh` renders `packaging/$LABEL.plist`)
  • `src/keychain.zig` — the `service` constant
• Notes `src/info_plist.zig` is only a doc comment (real value embedded from `Info.plist`), so it's accuracy-only.

Doc-only change; no code or build touched.

🤖 Generated with Claude Code