ci: add brand-name check for 'VelaClaw' in Markdown

[tanghao-xiaomi]

Summary

Add a lightweight PR check that fails when the CamelCase brand form VelaClaw appears in any Markdown file. The convention is to use openvelaClaw (lowercase openvela prefix, capital C) as the brand name in prose, to reduce trademark risk.

The check is intentionally case-sensitive and does not flag the following, which are real framework API / macro names and must remain unchanged:

• lowercase code identifiers: velaclaw, @system.velaclaw, velaclaw_client_open, velaclaw_ask
• uppercase macro: VELACLAW_DAEMON

Behavior

• Trigger: pull_request (opened / reopened / synchronize).
• Scans all *.md files with a plain case-sensitive grep.
• On match: emits GitHub Actions ::error file=...,line=... annotations pointing at each offending line, prints a summary that names the allowed form and the identifiers that are intentionally exempt, and fails the job.
• On no match: prints an OK line and passes.

Scope

• Single new file: .github/workflows/brand-name-check.yml
• No other files changed. Documentation-only enforcement.

⚠️ Merge order (important)

This check depends on #636 (the brand rename in mini_memo_guide.md) being merged first. If this workflow lands before #636, every subsequent PR against dev-ai-contest-2026 would fail this check because the base branch still contains the 18 VelaClaw occurrences that #636 removes.

Suggested sequencing:

1. Merge docs(mini_memo): use openvelaClaw brand name to reduce trademark risk #636 (brand rename).
2. Merge this PR (CI enforcement).

[tanghao-xiaomi]

Superseded by #638, which combines the rename and the CI check into a single PR. Closing this one.