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/detect_pollution.go

@@ -14,18 +14,28 @@ import (
 
 var detectPollutionCmd = &cobra.Command{
 	Use:   "detect-pollution",
-	Short: "Detect test issues that leaked into production database",
-	Long: `Detect test issues using pattern matching:
-- Titles starting with 'test', 'benchmark', 'sample', 'tmp', 'temp'
-- Sequential numbering (test-1, test-2, ...)
-- Generic descriptions or no description
-- Created in rapid succession
+	Short: "Detect and optionally clean test issues from database",
+	Long: `Detect test issues that leaked into production database using pattern matching.
 
-Example:
+This command finds issues that appear to be test data based on:
+- Titles starting with 'test', 'benchmark', 'sample', 'tmp', 'temp'
+- Sequential numbering patterns (test-1, test-2, ...)
+- Generic or missing descriptions
+- Created in rapid succession (potential script/automation artifacts)
+
+USE CASES:
+- Cleaning up after testing in a production database
+- Identifying accidental test data from CI/automation
+- Database hygiene after development experiments
+- Quality checks before database backups
+
+EXAMPLES:
   bd detect-pollution                 # Show potential test issues
   bd detect-pollution --clean         # Delete test issues (with confirmation)
   bd detect-pollution --clean --yes   # Delete without confirmation
-  bd detect-pollution --json          # Output in JSON format`,
+  bd detect-pollution --json          # Output in JSON format
+
+NOTE: Review detected issues carefully before using --clean. False positives are possible.`,
 	Run: func(cmd *cobra.Command, _ []string) {
 		// Check daemon mode - not supported yet (uses direct storage access)
 		if daemonClient != nil {