Fix P0 bug: JSONL lookup now returns LAST match (bd-58c0)

Addresses code review feedback:

✅ P0 (Must Fix):
- Fix JSONL lookup to return LAST match, not FIRST (resurrection.go:160-162)
  - Changed from early return to scan all matches and keep last
  - Respects JSONL append-only semantics

✅ P1 (Should Fix):
- Add test for multiple JSONL versions
  - TestTryResurrectParent_MultipleVersionsInJSONL verifies correct behavior
- Document error message change in CHANGELOG.md
  - Old: "parent issue X does not exist"
  - New: "parent issue X does not exist and could not be resurrected from JSONL history"
  - Marked as breaking change for script parsers

✅ P2/P3 (Nice to Have):
- Add documentation to AGENTS.md explaining auto-resurrection behavior
- Document best-effort dependency resurrection

⏸️ Deferred (P1 - Optimize batch resurrection):
- Caching optimization deferred (no batch use cases currently)

All tests pass:
- Unit tests: internal/storage/sqlite/
- Integration test: TestImportWithDeletedParent

internal/storage/sqlite/resurrection.go

@@ -133,6 +133,7 @@ func (s *SQLiteStorage) findIssueInJSONL(issueID string) (*types.Issue, error) {
 	scanner.Buffer(buf, maxCapacity)
 	
 	lineNum := 0
+	var lastMatch *types.Issue
 	for scanner.Scan() {
 		lineNum++
 		line := scanner.Text()
@@ -156,9 +157,10 @@ func (s *SQLiteStorage) findIssueInJSONL(issueID string) (*types.Issue, error) {
 			continue
 		}
 		
-		// Check if this is the issue we're looking for
+		// Keep the last occurrence (JSONL append-only semantics)
 		if issue.ID == issueID {
-			return &issue, nil
+			issueCopy := issue
+			lastMatch = &issueCopy
 		}
 	}
 	
@@ -166,7 +168,7 @@ func (s *SQLiteStorage) findIssueInJSONL(issueID string) (*types.Issue, error) {
 		return nil, fmt.Errorf("error reading JSONL file: %w", err)
 	}
 	
-	return nil, nil // Not found
+	return lastMatch, nil // Returns last match or nil if not found
 }
 
 // TryResurrectParentChain recursively resurrects all missing parents in a hierarchical ID chain.