fix: prevent internal fields from being exported to JSONL

ContentHash and SourceRepo were being exported to beads.jsonl even though
they are internal database fields. This caused JSONL pollution where every
issue got these extra fields, and re-exports would produce different output
than the original clean JSONL.

Changed JSON tags from `json:"...,omitempty"` to `json:"-"` for:
- ContentHash: Internal optimization field for content-based diffing
- SourceRepo: Internal metadata for multi-repo support

This fixes the ZFC resurrection bug where re-exports after import would
pollute the JSONL with internal fields.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/types/types.go

@@ -10,7 +10,7 @@ import (
 // Issue represents a trackable work item
 type Issue struct {
 	ID                 string         `json:"id"`
-	ContentHash        string         `json:"content_hash,omitempty"` // SHA256 hash of canonical content (excludes ID, timestamps)
+	ContentHash        string         `json:"-"` // Internal: SHA256 hash of canonical content (excludes ID, timestamps) - NOT exported to JSONL
 	Title              string         `json:"title"`
 	Description        string         `json:"description"`
 	Design             string         `json:"design,omitempty"`
@@ -29,7 +29,7 @@ type Issue struct {
 	CompactedAt        *time.Time     `json:"compacted_at,omitempty"`
 	CompactedAtCommit  *string        `json:"compacted_at_commit,omitempty"` // Git commit hash when compacted
 	OriginalSize       int            `json:"original_size,omitempty"`
-	SourceRepo         string         `json:"source_repo,omitempty"` // Which repo owns this issue (multi-repo support)
+	SourceRepo         string         `json:"-"` // Internal: Which repo owns this issue (multi-repo support) - NOT exported to JSONL
 	Labels             []string       `json:"labels,omitempty"` // Populated only for export/import
 	Dependencies       []*Dependency  `json:"dependencies,omitempty"` // Populated only for export/import
 	Comments           []*Comment     `json:"comments,omitempty"`     // Populated only for export/import