chore: add anti-spam guard for star-farming issues

[liukewia]

Summary

Adds an automated Anti-spam Issue Guard GitHub Actions workflow (.github/workflows/anti-spam-issues.yml) to automatically flag, comment on, and close suspicious issues—specifically targeting coordinated star-farming accusations and bot spam originating from new accounts with no prior repository activity.

Key Capabilities

• Trigger Support: Automatically runs on new issue creation (issues: opened) or via manual trigger (workflow_dispatch) with an issue number input.
• Trust & Whitelisting Rules: Bypasses repository collaborators, owners, contributors, members, bot accounts, and users with prior issue or PR activity in the repository.
• Account Age Threshold: Checks if the author's account age is within the configured threshold (default: 180 days).
• Pattern Matching: Detects combinations of star-farming keywords, abnormal growth claims, bot account patterns, report threats, metric mismatches, and reputation attack phrases.
• Automated Triage: Labels flagged issues with pending-maintainer-review, posts a friendly bilingual (English/Chinese) explanation asking genuine users to comment, and automatically closes the issue as not_planned.

Target branch

• Base is develop (feature / fix — default)
• Base is main (release/* or hotfix/* only)

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Refactor / chore
• Release / hotfix

Test plan

• Triggered manually via workflow_dispatch on test issue numbers (#19 format and raw integer format).
• Verified user bypass logic against trusted members and accounts with previous activity.
• Tested Regex pattern hits against sample spam text matching star-farming templates.
• Verified successful labeling, commenting, and issue closing behavior via Octokit REST API.
• make all passes locally
• Added/updated tests

Checklist

• Updated CHANGELOG.md (if user-facing)
• README / docs updated (if needed)