feat(cli): add effectCmd wrapper + convert models command

[kitlangton]

Summary

First step toward Effect-native CLI commands. Adds an `effectCmd` wrapper that lets handler bodies be `Effect`s with services yieldable and tracing spans baked in — and converts `models.ts` as the first end-to-end smoke test.

Why

Today every CLI handler is the same Promise/ALS shape:
```ts
async handler(args) {
await Instance.provide({ // Promise wrapper, ALS bind
directory: process.cwd(),
async fn() {
const project = Instance.project // ALS read
await AppRuntime.runPromise( // Promise→Effect→Promise→Effect dance
Service.use((s) => s.method(...)) // for ONE call
)
if (...) process.exit(1) // ad-hoc exit
}
})
}
```

After:
```ts
handler: Effect.fn("Cli.")(function* (args) {
const ctx = yield* InstanceRef
const svc = yield* Service // yield once, use many
if (...) return yield* fail("message") // domain error → clean exit
...
})
```

What's in the wrapper

• `InstanceStore.provide({directory: ...}, effect)` so `InstanceRef` is bound for the handler body
• `AppRuntime.runPromise(...)` so any `AppServices` (Config, Provider, Git, MCP, Plugin, Bus, etc.) can be yielded directly
• `Effect.catchTag("CliError", ...)` translates `fail("...")` into a printed error + non-zero exit
• Handler is typically an `Effect.fn("Cli.")(function*(args) { ... })` value, giving each CLI invocation a named OTel span automatically

Path to effect/cli

`effectCmd` is a stepping stone. Once all 18 CLIs use it, swapping the underlying `cmd()` factory for `effect/cli`'s `Command.make(...)` doesn't touch the handler bodies — only the args parser changes (yargs `Argv` → effect/cli `Args.*`).

Numbers

• New helper: 54 lines (`src/cli/effect-cmd.ts`)
• `models.ts`: 88 → 66 lines (-25%)
• Each subsequent CLI conversion is a net reduction; helper cost is amortized

Smoke tests

• `bun run dev models` — prints model list ✓
• `bun run dev models nonexistent-provider` — prints error, exits 1 ✓
• `bun run typecheck` — clean

Followup

Convert remaining 17 CLIs (`pr`, `mcp`, `github`, `plug`, `agent`, `providers`, `debug/*`, `import`, `stats`, etc). They follow the same pattern; can be batched 4-5 per PR or swarmed by directory.