fix(cli): make required_version advisory, warn on eval failure instead of prompting/exiting

[christso]

Summary

• Make required_version mismatches advisory by default: warn once, never prompt, self-update, or exit unless --strict is explicitly used.
• Surface a failure-time eval summary note when results have quality failures or execution errors and the installed version does not satisfy required_version.
• Update serve/Dashboard comments, self-update header docs, public docs, and tests for the new contract.

Verification

• bun run verify

Manual UAT

Temp project used .agentv/config.yaml with required_version: ">=999.0.0", a mock target, and deterministic contains assertions.

Red (origin/main):

• failing eval exited 1 from threshold failure and printed RESULT: FAIL, but no summary note about the version mismatch.
• passing eval exited 0; mismatch warning was stderr-only.
• TTY path hung after the mismatch warning until killed, demonstrating the old prompt path.

Green (this branch):

• failing eval exited 1 from threshold failure and printed the version mismatch note in the summary.
• passing eval exited 0 with no summary note, only one low-noise stderr warning.
• TTY passing eval completed with no prompt, self-update, or version-based exit.

Failure-time note observed:

note: agentv 4.38.0 does not satisfy this project's required_version >=999.0.0 - this may be the cause. Run `agentv self update`.

Closes #1395

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