chore(cli-v2): un-ignore CLI source tree for binary release workflow

The CLI source (242 files, ~14k lines) was gitignored during the
earlier cli→cli-v2 reorg so only the published npm package carried it.
That blocks the GitHub Actions release workflow (release-cli.yml),
which clones the repo fresh on each runner and needs the source to
compile binaries via `bun build --compile`.

Moves the gitignore from root-level to `apps/cli-v2/.gitignore` with
only the usual build artefacts excluded (node_modules, dist, .turbo,
.cache). Source is now in git at apps/cli-v2/src/.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/cli-v2/biome.json

@@ -0,0 +1,4 @@
+{
+  "$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
+  "extends": ["../../biome.json"]
+}