pm validate should detect duplicate logical issue code prefixes (e.g., ISSUE-####) #235

Summary

The pm tracker can contain multiple items with the same logical issue code prefix (for example ISSUE-004) because title conventions are not validated, which weakens auditability and causes ambiguity for governance and duplicate detection workflows.

Evidence

During a full tracker pass in 2d-bots I detected duplicate logical issue identifiers in open/closed item titles:

• pm-0thx: ISSUE-004: No CI/CD Pipeline - Zero GitHub Actions Workflows (closed)
• pm-52eu: ISSUE-004: No i18n/L10n Strategy for Multi-Language Support (open, now observed before rename)

This required a manual rename to avoid ambiguity and left an implicit governance gap in pm history and reporting.

Expected Behavior

pm should support a built-in validation check that detects duplicate semantic identifiers embedded in titles.

At minimum, add a check to pm validate that:

• scans title prefixes by namespace (ISSUE-####, FEATURE-##, etc.), where applicable,
• reports duplicates regardless of item status,
• can be configured per project schema (strict/progressive modes),
• provides stable remediation guidance in command output.

Reproduction

1. Create or update multiple items with the same conventional prefix but different titles.
2. Run pm validate (currently this should pass).
3. Detect ambiguity only via manual search, not via standard validate output.

Suggested Fix

• Add a --check-unique-title-prefixes or extend existing metadata validation to include title-prefix collision checks.
• Add optional normalization config for accepted prefixes to avoid false positives.
• Include this check in tracker health or quality audits so collisions are caught during CI.

Impact

This closes a class of PM governance defects and improves deterministic project-context semantics, especially in large ecosystems with >1000 items.