feat(discovery): add convention file discovery and config types

[vapi-tasker]

Summary

• Adds foundation for dynamic project checks feature (VAP-11695)
• New ConventionsConfig and DiscoveryConfig interfaces in config.ts
• Extended ChecksConfig with lint, format, build boolean flags
• Extended CommandsConfig with lint, format, build (nullable) commands
• New conventions.ts module for discovering convention files:
  • Discovers CLAUDE.md, .cursorrules, .cursor/rules, .claude/settings
  • Priority-based loading with size limits (100KB/file, 200KB combined)
  • Deduplication of similar content blocks
  • UTF-8 text validation and circular symlink detection

Part 1 of 4 for VAP-11695

This PR establishes the config types and convention discovery module. Subsequent PRs will add:

• PR fix: add atlas parity - regex patterns, rules guidance, dotenv loading #2: Script discovery module
• PR docs: add comprehensive setup guide for BULLETPROOF #3: Discovery index and tests
• PR fix: enable npm publishing by setting private to false #4: Integration into guardian, runner, prompt, analyzer

Test plan

• TypeScript compilation passes
• Existing tests continue to pass
• New convention discovery logic tested in PR docs: add comprehensive setup guide for BULLETPROOF #3

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Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com