CLI/TUI: add source coverage gates (in-process runCli + TUI flows) #1484

Carved out from the "did not solve" list of #1452 (port of CLI/TUI/launcher to v2).

Problem

The per-file coverage gate (lines ≥ 90, etc.) is enforced only by the web vitest suite (web src + core). CLI tests run out-of-process — they spawn node build/index.js via cli-runner.ts — so coverage instrumentation never sees clients/cli/src/cli.ts. The TUI has only 2 smoke tests. Net: CLI/TUI source has no coverage gate, so regressions there are invisible to CI.

Proposed solution

• Add an in-process runCli() entry so tests can import and exercise CLI logic under coverage instrumentation, keeping a thin out-of-process E2E layer for the real binary.
• Add a vitest coverage config + per-file gate for clients/cli/src (and clients/tui/src as feasible — expand tui-servers.ts and Ink flow tests).
• Wire the gates into CI as their own steps.

Acceptance criteria

• CLI source is exercised in-process with coverage measured (not just spawned subprocess E2E).
• A per-file coverage gate is enforced for CLI (and TUI where feasible), matching the web thresholds or a documented interim target.
• CI fails when CLI/TUI source coverage drops below the gate.