feat(cli): add version check to studio/serve commands

[christso]

Summary

• Enforce required_version from .agentv/config.yaml before starting AgentV Studio (agentv studio / agentv serve), matching the existing agentv eval behavior.
• Interactive (TTY) runs prompt "Update now? (Y/n)"; non-interactive runs warn to stderr and continue.
• Single-project scope only — multi-project server deployments remain out of scope (tracked in feat(cli): self update should update the same binary location (local vs global) #1127).

Implementation

apps/cli/src/commands/results/serve.ts — call enforceRequiredVersion() (from version-check.ts) before the server is started, using loadConfig() + findRepoRoot() to locate the project's .agentv/config.yaml (same pattern as run-eval.ts:988-992).

The check runs after benchmark-management subcommands (--add / --remove / --discover) so those paths aren't affected.

Red/Green UAT

Red (on main): agentv studio with a mismatched required_version: ">=99.0.0" launched silently — no warning, no prompt. Output:

No results found. Dashboard will show an empty state.
Run an evaluation to see results: agentv eval <eval-file>
Dashboard: http://localhost:31170
Benchmarks API: http://localhost:31170/api/benchmarks
Press Ctrl+C to stop

Green (this branch):

1. Non-interactive (stdin redirected) with required_version: ">=99.0.0":

   STDERR:
   Warning: This project requires agentv >=99.0.0 but you have 4.20.0.
     Run `agentv self update` to upgrade.
   

   Server starts normally after the warning.

2. Interactive TTY (via script), user answers n:

   Warning: This project requires agentv >=99.0.0 but you have 4.20.0.
   ? Update now? (Y/n) n
   ✔ Update now? No
   No results found. Dashboard will show an empty state.
   Dashboard: http://localhost:31172
   

   User declines; server starts as before.

3. Satisfying range (required_version: ">=4.0.0"): no warning, no prompt — server starts silently.

4. No .agentv/config.yaml: no warning, server starts silently.

Test plan

• Existing serve unit tests (39 tests) pass
• Typecheck, build, lint, full test suite (via pre-push hooks)
• Manual UAT: red/green above

Closes #1128

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