refactor(cli): convert run command to effectCmd

[kitlangton]

Summary

Stage 3 of the run.ts conversion (Stage 1 is #25517 — function-form `instance`).

• `cmd()` → `effectCmd({ instance: (args) => !args.attach, directory: ... })`
  • `--attach` path: no instance load (matches legacy — legacy didn't load either; SDK talks to the remote server)
  • default path: instance loaded by `effectCmd` via `InstanceStore.provide`, auto-disposed on exit (matches legacy `bootstrap()` finally)
• Drop the `bootstrap(process.cwd(), async () => {...})` wrapper since `effectCmd` handles it now.
• The entire legacy handler body is wrapped in `Effect.promise()` inside `Effect.fn` for byte-equivalent behavior. `process.exit(1)` paths and the internal `AppRuntime.runPromise(Agent.Service.use(...))` agent-validation call all preserved as-is.

Also extends `effectCmd` to type `handler` args as `WithDoubleDash` so `args["--"]` (yargs's "everything after `--` separator") works without casts. Matches the legacy `cmd()` wrapper's shape.

Why this conversion is safe

The `Effect.promise(async () => { ... })` wrap means the handler body executes as a Promise inside the Effect runtime — same async semantics as legacy `async (args) => { ... }`. No behavior change to:

• arg parsing, file resolution, validation, `process.exit(1)` paths
• session/share/execute/loop closures
• agent validation (`sdk.app.agents` for `--attach`, `AppRuntime.runPromise(Agent.Service.use)` for default)
• SDK construction (`createOpencodeClient` with remote URL or local fetch)

Stacked on #25517

Depends on the function-form `instance` opt-out landing first.

Test plan

• `bun run typecheck`
• `bun run test test/cli/` — 137 pass
• `run` (no args) → `Error: You must provide a message or a command` exit 1
• `run --fork "hi"` → `Error: --fork requires --continue or --session` exit 1
• `run --file /tmp/nonexistent.txt "hi"` → `Error: File not found: ...` exit 1
• `run --attach http://127.0.0.1:1 "hi"` → connects, no instance load, fails gracefully → `Error: Session not found` exit 1