pixtuoid: Command for GitHub Copilot

Add a new agent-CLI Source

Wire up a new agent CLI (${input:name}) as a pixtuoid Source. This is not a single-file change — read crates/pixtuoid-core/CLAUDE.md ("multi-source decoding" / "Adding a new agent CLI") first, then:

1. Implement the Source trait (hook-only CLI? skip it + the runtime wiring — set transcript: None and ship a hook.custom decoder + install target instead). Per-source JSONL format knowledge lives in the source's own decoder fn (injected into JsonlWatcher via fn pointers), not a shared decoder.
2. Add ONE SourceDescriptor row in source/registry.rs (label prefix, decoders, hook keying, reducer caps) — its name field IS the roster (registered_source_names() projects REGISTRY; uniqueness pinned by registered_source_names_are_unique), and the conformance test forces a coalescing fixture.
3. Wire it into runtime/driver.rs::build_source_set (the one construction site, called by run_async) — the registry gates conformance tests, not spawning, but a bridge test (build_source_set_wires_every_transcript_bearing_source_plus_the_hook_router) pins that set to the registry's transcript-bearing rows, so a registered-but-unwired source fails just test.
4. If you add an AgentEvent variant, add a matching arm to AgentEvent::agent_id() in source/mod.rs.
5. Update the four test areas that exercise the channel / Source / reducer together: tests/reducer/, tests/e2e.rs, tests/transport/socket.rs, tests/watcher/, plus runtime/driver.rs on the binary side.
6. Add a captured fixture under tests/sources/fixtures/<name>/<scenario>/ (a unique lifecycle also gets a tests/sources/<cli>.rs module). The test layout + add-a-CLI steps are in crates/pixtuoid-core/tests/CLAUDE.md.
7. Add a row to site/src/sources.json (the tool × OS matrix + README glimpse); tests/supported_sources_manifest.rs pins its supported set to registered_source_names(), so a new source fails that test until the row exists. Then just gen-readme to sync the README's Supported Tools section.
8. Add the per-source badge hue: a Theme::source (SourceColors) field in EVERY theme file + a match arm in tui/widgets/dashboard.rs::dashboard_line (every_registry_source_has_a_non_fallback_badge_color + source_colors_cover_every_registered_source fail otherwise).
9. If the CLI has a custom config/home root, add a pub fn <cli>_home() honoring its *_HOME env precedence, called from BOTH the watcher's default_paths() AND the installer's default_config_path() (one function, two consumers).
10. Cover the source in the binary's TWO per-source INTEGRATION goldens (own test binaries, NOT built by -p pixtuoid --lib): regenerate the sources --json golden crates/pixtuoid/tests/snapshots/cli/sources.json (SNAPSHOTS=overwrite cargo test -p pixtuoid --test cli_json), and add a WireCase + per-source render test in crates/pixtuoid/tests/wire_to_pixels.rs (hook-only → DecodeKind::Hook+Transport::Hook), else sources_json_lists_every_source_in_an_isolated_home / wire_matrix_covers_every_registered_source red.

These cross-crate deps are caught only by just preflight's FULL run, not the targeted source/install suites — and a -p <crate> --lib run builds NEITHER integration binary in step 10 (kimi #692 shipped both red past a green --lib run and a multi-lens review). Respect the architecture invariants (no terminal deps in pixtuoid-core/pixtuoid-scene; one (Transport, AgentEvent) channel) and .github/instructions/rust.instructions.md. Run just preflight (or at least cargo nextest run --workspace) before the PR.