feat(apps/cli): first rust binary on new layout — ctm metrics end-to-end (task #143 slice 1)

[joelteply]

First slice of task #143 (Rust-first clients — rewrite jtag CLI in Rust). The apps/cli slot was a placeholder README per the Stage 1-2.5 layout sweep; this PR lands the first real rust binary on it.

What lands

apps/cli/
├── Cargo.toml            new crate, binary name `ctm`
├── README.md             status / install / usage / architecture
└── src/main.rs           clap CLI + Connection::connect + metrics subcmd

Workspace member added at root Cargo.toml under a new apps/ tier section (sibling to client/).

One subcommand wired end-to-end

$ ctm metrics --peer <substrate-uuid>
{
  "modules": [...],
  "count": N
}

The wire path:

1. Cli::parse() extracts --peer / --home / CONTINUUM_PEER_ID / CONTINUUM_AIRC_HOME.
2. Airc::open($HOME/.airc) opens the human's airc citizen.
3. Connection::connect(Arc::new(airc), peer_uuid) builds the substrate session.
4. .commands().execute("runtime/metrics/all", {}) round-trips through AircIpcTransport.
5. continuum-core-server's CommandRequestHandler::parse_envelope decodes, RuntimeModule dispatches, send_reply ships the response.

Every byte of that path is the SAME path core/continuum-core/tests/airc_ipc_roundtrip.rs verifies — no new wire, just a new caller.

Why this matters

• First rust binary in the apps/ tier — proves the substrate-first architecture works end-to-end from a real binary.
• Same continuum-client seam every future apps/{web, mcp, mobile, ar, vr, desktop} will consume.
• Migration path for ./jtag is now incremental: each future PR adds one ctm <subcommand>, the Node ./jtag shrinks.

Verified

cargo build -p continuum-cli           → clean (31s cold, 2s incremental)
ctm --help                             → prints usage cleanly
ctm metrics                            → typed error: "--peer is required"

Runtime tests against a live substrate are a follow-up — the wire path is already proven by the integration test that just merged.

Pending follow-ups (in README.md)

• Auto peer discovery (read ~/.continuum/peer.json or airc ipc-endpoint).
• More subcommands (chat/send, gpu/stats, data/list, persona/list).
• Shell shim install (tools/scripts/install-cli.sh, jtag alias).

Test plan

• cargo build -p continuum-cli
• ctm --help
• ctm metrics (without --peer; typed error)
• ctm metrics against a running continuum-core-server (manual)
• CI green