feat(rules): add no-brittle-hardcoding agent rule

[andrei-hasna]

Summary

• add the mandatory no-brittle-hardcoding coding-agent rule to the canonical global system prompt, non-overridable global rules, and Hasna Agent Operating Rules
• bump the source set to 2026-07-10 and agent operating rules to v1.1.3
• update docs/changelog/tests to assert Codewith and Antigravity exports include the rule

Validation

• bun run typecheck
• bun test
• bun run build
• bun run vendor-kit:check
• identities canonical export smoke for codewith and antigravity includes the no-hardcoding rule
• gitleaks git --staged --redact --no-banner --no-color .
• gitleaks git --log-opts HEAD~1..HEAD --redact --no-banner --no-color .