Remove legacy inline HTML dashboard and serve alias

[christso]

Objective

Remove the legacy inline HTML dashboard from serve.ts and the fallback logic in createApp(). The React SPA (apps/studio/) fully replaces it. The dashboard has never been published, so there are no backward-compat concerns.

Context

PR #806 scaffolded apps/studio/ (React SPA) and renamed agentv serve → agentv studio. The old dashboard was a ~1000-line generateServeHtml() function that inlined all HTML/CSS/JS as template strings in apps/cli/src/commands/results/serve.ts. The SPA fallback path in createApp() still calls generateServeHtml() if the studio dist directory isn't found.

Scope

Delete

• generateServeHtml() function and all its helpers (inline CSS, JS template strings) in serve.ts
• The fallback branch at the '/' route in createApp():

  // Delete this fallback:
  return c.html(generateServeHtml(results, sourceFile));

Simplify

• createApp() route for '/': serve studioDistPath/index.html or throw a clear error:

  Error: Studio dist not found. Run "bun run build" to build the SPA.
  

• Remove the studioDir?: string | false option if it was only used to disable SPA serving for the inline fallback. Check if tests rely on it — if so, update tests to build studio first or mock the dist path.
• Remove the serve alias — studio is the only command name. No backward-compat needed since dashboard was never published.

Keep

• All API routes (/api/runs, /api/feedback, /api/index, /api/results/:filename, static asset serving)
• resolveStudioDistDir() — still needed to locate the built SPA
• The studio command registration in cli.ts

Acceptance signals

• generateServeHtml and inline HTML/CSS/JS template strings are deleted from serve.ts
• agentv studio errors clearly if studio dist is missing (not a silent fallback)
• agentv serve alias is removed
• Existing tests pass (update any that relied on studioDir: false or generateServeHtml)
• bun run build && bun apps/cli/src/cli.ts studio still serves the React SPA

Non-goals

• No new features — this is pure cleanup
• Don't restructure API routes or change the Hono app shape
• Don't rename the package or command

Related

• feat: scaffold AgentV Studio with convex-evals dashboard feature parity #805 — Studio scaffold tracking issue
• feat(studio): scaffold AgentV Studio SPA with dashboard feature parity #806 — Studio scaffold PR (adds apps/studio/, renames serve → studio)