feat: Complete command set standardization (bd-au0)

Epic bd-au0: Command Set Standardization & Flag Consistency

Completed all 10 child issues:

P0 tasks:
- Standardize --dry-run flag across all commands (bd-au0.1)
- Add label operations to bd update (bd-au0.2)
- Fix --title vs --title-contains redundancy (bd-au0.3)
- Standardize priority flag parsing (bd-au0.4)

P1 tasks:
- Add date/priority filters to bd search (bd-au0.5)
- Add comprehensive filters to bd export (bd-au0.6)
- Audit and standardize JSON output (bd-au0.7)

P2 tasks:
- Improve clean vs cleanup documentation (bd-au0.8)
- Document rarely-used commands (bd-au0.9)

P3 tasks:
- Add global verbosity flags --verbose/-v and --quiet/-q (bd-au0.10)

Key changes:
- export.go: Added filters (assignee, type, labels, priority, dates)
- main.go: Added --verbose/-v and --quiet/-q global flags
- debug.go: Added SetVerbose/SetQuiet and PrintNormal helpers
- clean.go/cleanup.go: Improved documentation with cross-references
- detect_pollution.go: Added use cases and warnings
- migrate_hash_ids.go: Marked as legacy command
- rename_prefix.go: Added use cases documentation

All success criteria met: flags standardized, feature parity achieved,
naming clarified, JSON output consistent.

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

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

cmd/bd/cleanup.go

@@ -13,8 +13,11 @@ import (
 
 var cleanupCmd = &cobra.Command{
 	Use:   "cleanup",
-	Short: "Delete all closed issues (optionally filtered by age)",
-	Long: `Delete all closed issues to clean up the database.
+	Short: "Delete closed issues from database to free up space",
+	Long: `Delete closed issues from the database to reduce database size.
+
+This command permanently removes closed issues from beads.db and beads.jsonl.
+It does NOT remove temporary files - use 'bd clean' for that.
 
 By default, deletes ALL closed issues. Use --older-than to only delete
 issues closed before a certain date.
@@ -34,7 +37,10 @@ SAFETY:
 - Requires --force flag to actually delete (unless --dry-run)
 - Supports --cascade to delete dependents
 - Shows preview of what will be deleted
-- Use --json for programmatic output`,
+- Use --json for programmatic output
+
+SEE ALSO:
+  bd clean      Remove temporary git merge artifacts`,
 	Run: func(cmd *cobra.Command, args []string) {
 		force, _ := cmd.Flags().GetBool("force")
 		dryRun, _ := cmd.Flags().GetBool("dry-run")