feat: enforce fixing all issues regardless of authorship

Adds a mandatory "No Pre-Existing Issue Exceptions" policy to prevent
Claude from dismissing errors, warnings, or linting failures it didn't
write. Also extends the code-reviewer agent with an Issue Ownership
Policy requiring concrete fixes rather than passive reporting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/CLAUDE.md

@@ -81,6 +81,34 @@ terraform plan                  # Preview changes
 
 **This is not optional. Treat refactor-scan invocation with the same priority as running tests.**
 
+## No "Pre-Existing Issue" Exceptions (MANDATORY)
+
+**There is no such thing as a pre-existing issue that can be skipped.**
+
+If you encounter any error, warning, linting failure, type error, or test failure — regardless of whether you wrote the code — you MUST fix it.
+
+**These phrases are banned:**
+- "This is an existing issue, not part of my change"
+- "This was already present before my changes"
+- "Out of scope for this task"
+- "I'll leave this for a separate PR"
+
+**What to do instead:**
+1. Fix it immediately in the same session
+2. If the fix is genuinely large (e.g. a systemic architecture problem), create a tracked TODO comment in the code AND note it explicitly to the user — but still fix any small instances you can
+3. Never add suppression comments (`# noqa`, `// eslint-disable`, `@ts-ignore`, `#[allow(...)]`) to hide an issue rather than fix it
+4. If a suppression is genuinely warranted (e.g. a known upstream bug), document exactly why in the suppression comment
+
+**This applies to:**
+- Test failures discovered while running the suite
+- Linting errors and warnings in files you open or modify
+- Type errors surfaced by the type checker
+- Compiler/interpreter warnings
+- Security issues found incidentally
+- Deprecation warnings
+
+**The codebase is your responsibility, not just the lines you added this session.**
+
 ## Coverage Requirements
 
 | Layer | Target | Notes |