fix: replace PRODUCT-TRUTH.md/ARCHITECTURE.md refs with AGENTS.md

These docs never existed — gardener and review-pr referenced them
as if they did. AGENTS.md tree is now the single architecture
reference for all agents.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gardener/best-practices.md

@@ -21,7 +21,7 @@ A "ready" issue has:
 ## When to escalate (NEVER decide these)
 - Issue scope is ambiguous — could be interpreted multiple ways
 - Two issues overlap but aren't exact duplicates — need human to pick scope
-- Issue contradicts a design decision (check PRODUCT-TRUTH.md, ARCHITECTURE.md)
+- Issue contradicts a design decision (check AGENTS.md tree)
 - Issue is feature request vs bug — classification matters for priority
 - Closing would lose important context that isn't captured elsewhere
 

gardener/gardener-poll.sh

@@ -182,7 +182,7 @@ $(echo -e "$PROBLEMS")
 ## Primary mission: promote tech-debt → backlog
 Most open issues are raw review-bot findings labeled \`tech-debt\`. Your main job is to convert them into well-structured \`backlog\` items the dev-agent can execute. For each tech-debt issue:
 1. Read the issue body + referenced source files to understand the real problem
-2. Check docs/PRODUCT-TRUTH.md and docs/ARCHITECTURE.md for context
+2. Check AGENTS.md (and sub-directory AGENTS.md files) for architecture context
 3. Add missing sections: \`## Affected files\`, \`## Acceptance criteria\` (checkboxes, max 5), \`## Dependencies\`
 4. If the issue is clear and actionable → relabel: remove \`tech-debt\`, add \`backlog\`
 5. If scope is ambiguous or needs a design decision → ESCALATE with options