chore: update references after the linear-cli-ex -> linear-cli / linear-cli -> linear-cli-rb repo renames

[bougyman]

Background

Both GitHub repos were renamed:

• rubyists/linear-cli-ex (this repo, the Elixir port) -> rubyists/linear-cli
• rubyists/linear-cli (the old Ruby CLI, vendored at vendor/ruby-linear-cli) -> rubyists/linear-cli-rb

Local git remotes are already fixed (this repo's origin, and
vendor/ruby-linear-cli's remote in both .gitmodules and its own
checked-out git config) - verified both actually fetch against the
renamed repos, not just relying on GitHub's redirect. This issue is the
rest: every place that still hardcodes the old name.

Verified GitHub does 301-redirect github.com/rubyists/linear-cli-ex ->
github.com/rubyists/linear-cli right now, so nothing is actually broken
today - but redirects aren't permanent (reclaimable if anyone else takes
the old name later) and everything should say what it actually is.

Every hardcoded reference found (grepped app/, this repo's own files,

and the homebrew-tap submodule; app/lib has none - every repo-name-derived
value there is computed from git remote get-url origin at CI/script
time, not hardcoded, so it already follows the remote fix with zero code
changes)

• install.sh: repo=rubyists/linear-cli-ex (drives the release download
  URL) + state_dir=.../linear-cli-ex (a local state-dir name, not a URL)
• uninstall.sh: same state_dir name - must change identically to
  install.sh's, since uninstall only works by finding the same manifest
  path
• Readme.adoc: 9 occurrences - container image paths
  (ghcr.io/rubyists/linear-cli-ex), release download URLs, the git clone URL, and the install.sh/uninstall.sh curl-pipe URLs
• .github/workflows/main.yaml: one occurrence - the container job's
  saved-image temp tarball filename ($RUNNER_TEMP/linear-cli-ex.tar) -
  purely a local temp filename, cosmetic only, no functional effect
  either way
• vendor/rubyists-homebrew-tap/Formula/lc.rb: homepage + both release
  download URLs (separate repo - its own commit/PR)
• vendor/rubyists-homebrew-tap/Readme.adoc: one occurrence
• CHANGELOG.md: many historical release-please-generated links -
  deliberately excluded, see Decisions below

Decisions

1. Leave CHANGELOG.md's historical entries alone. They're
   release-please's own generated audit trail of what was true at each
   past release - this repo's own convention (AGENTS.md: "Initial
   Plan... historical snapshot - not edited after the fact") already
   treats history like this as immutable. GitHub's redirect keeps the old
   links working regardless. Future entries release-please generates will
   automatically use the current repo (it reads github.repository from
   the Actions context, which GitHub already updated on rename) - no
   config change needed.
2. Rename the state_dir now (~/.local/state/linear-cli-ex ->
   ~/.local/state/linear-cli), not kept for backward compat. The tool
   shipped its first real release only a day ago - real installs against
   the old name are minimal, and carrying a mismatched directory name
   forever for a near-zero-adoption compat concern isn't worth it.
3. ghcr.io/rubyists/linear-cli-ex images stay exactly where they are -
   GHCR packages are namespaced by whatever owner/name was used at push
   time, not auto-renamed alongside a repo rename (unlike github.com repo
   pages, which do redirect). Existing tags remain retrievable at the old
   path permanently; only document/push new tags at
   ghcr.io/rubyists/linear-cli going forward. ci/publish.sh needs no
   code change - IMAGE_NAME already derives from the checkout
   directory's basename, which will already read "linear-cli" the moment
   CI checks out the renamed repo.

Sequencing

1. install.sh + uninstall.sh (repo=/state_dir= - keep them
   consistent with each other).
2. Readme.adoc (all 9 occurrences).
3. .github/workflows/main.yaml's cosmetic tarball filename.
4. vendor/rubyists-homebrew-tap (its own commit/PR, since it's a
   separate repo): Formula/lc.rb + Readme.adoc, then bump this repo's
   submodule pointer to that commit.
5. Manually verify: ./install.sh/./uninstall.sh still round-trip with
   the renamed state_dir (same technique as Prefer Docker over Podman in container-image CI scripts #67's verification - a real
   run, not just reading the diff).