feat: add owner field for human attribution in HOP CV chains

Add 'owner' field to Issue struct for tracking the human responsible
for the issue, distinct from 'created_by' which tracks the executor.
Owner is populated from git author email (GIT_AUTHOR_EMAIL or git
config user.email), per Decision 008 for CV accumulation.

Changes:
- Add Owner field to types.Issue with omitempty JSON tag
- Include Owner in content hash computation
- Add owner column migration (036_owner_column.go)
- Update all SQL queries to include owner field
- Add getOwner() helper using git author email fallback chain
- Populate owner in bd create command
- Add owner to RPC CreateArgs protocol

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Executed-By: beads/crew/dave
Rig: beads
Role: crew

internal/rpc/protocol.go

@@ -98,6 +98,7 @@ type CreateArgs struct {
 	// ID generation
 	IDPrefix  string `json:"id_prefix,omitempty"`  // Override prefix for ID generation (mol, eph, etc.)
 	CreatedBy string `json:"created_by,omitempty"` // Who created the issue
+	Owner     string `json:"owner,omitempty"`      // Human owner for CV attribution (git author email)
 	// Molecule type (for swarm coordination)
 	MolType string `json:"mol_type,omitempty"` // swarm, patrol, or work (default)
 	// Agent identity fields (only valid when IssueType == "agent")