Add ignored extension support to AI reviewer

[shaiananvari8]

Summary

Adds --ignore-extensions to ai_reviewer.py so directory reviews can skip configured suffixes such as .py, .ts, .md, or .txt before file review work begins.

/claim #16

Changes

• Adds comma-separated ignored extension parsing with lowercase and leading-dot normalization.
• Filters supported review extensions before recursive or non-recursive directory collection.
• Skips a single-file review when that file's extension is ignored.
• Fixes existing invalid ReviewSeverity.HIGH references so the reviewer can be instantiated and exercised.
• Adds a focused validator covering normalization and directory filtering.
• Keeps build diagnostics running when npm is unavailable locally.

Testing

• python -m py_compile build.py tools/ai_reviewer.py tools/validate_ai_reviewer_ignore_extensions.py
• python tools/validate_ai_reviewer_ignore_extensions.py
• git diff --check origin/main...HEAD
• python build.py generated diagnostic/build-16b0f8d9.json and diagnostic/build-16b0f8d9.logd; module builds failed locally because this Windows environment does not have the repo language toolchains installed, and those failures are recorded in the diagnostic metadata.

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

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• I would like to request that my diagnostic build log is removed before merging

[opirebot]

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