Complete bd-175, bd-176, bd-177: Memory tests, corruption docs, prefix validation

- bd-175: Added comprehensive test coverage for internal/storage/memory backend
  - All CRUD operations, dependencies, labels, comments
  - Thread safety with race detection
  - LoadFromIssues and counter sync
  - Fixed batch duplicate detection

- bd-176: Documented corruption vs collision distinction
  - Added FAQ entry explaining logical vs physical corruption
  - Updated TROUBLESHOOTING with clear guidance
  - Clarified when to use collision resolution vs reimport

- bd-177: Added prefix validation in SQLite mode
  - Validates explicit IDs match configured prefix
  - Works in both CreateIssue and CreateIssues
  - Comprehensive tests for single and batch operations

TROUBLESHOOTING.md

@@ -92,18 +92,29 @@ bd import -i .beads/issues.jsonl
 
 ### Database corruption
 
-If you suspect database corruption:
+**Important**: Distinguish between **logical consistency issues** (ID collisions, wrong prefixes) and **physical SQLite corruption**.
+
+For **physical database corruption** (disk failures, power loss, filesystem errors):
 
 ```bash
 # Check database integrity
 sqlite3 .beads/*.db "PRAGMA integrity_check;"
 
-# If corrupted, reimport from JSONL
+# If corrupted, reimport from JSONL (source of truth in git)
 mv .beads/*.db .beads/*.db.backup
 bd init
 bd import -i .beads/issues.jsonl
 ```
 
+For **logical consistency issues** (ID collisions from branch merges, parallel workers):
+
+```bash
+# This is NOT corruption - use collision resolution instead
+bd import -i .beads/issues.jsonl --resolve-collisions
+```
+
+See [FAQ](FAQ.md#whats-the-difference-between-sqlite-corruption-and-id-collisions) for the distinction.
+
 ### Multiple databases detected warning
 
 If you see a warning about multiple `.beads` databases in the directory hierarchy: