feat: add bd admin parent command for cleanup/compact/reset (bd-3u8m)

Move cleanup, compact, and reset commands under `bd admin` namespace.
Creates hidden aliases for backwards compatibility that show deprecation
notice when used.

- Create cmd/bd/admin.go with parent command
- Create cmd/bd/admin_aliases.go for hidden backwards-compat aliases
- Update cleanup.go, compact.go, reset.go to remove rootCmd.AddCommand
- Update all documentation to use `bd admin <cmd>` syntax

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

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

docs/CLI_REFERENCE.md

@@ -296,10 +296,10 @@ bd --actor alice <command>
 
 ```bash
 # Clean up closed issues (bulk deletion)
-bd cleanup --force --json                                   # Delete ALL closed issues
-bd cleanup --older-than 30 --force --json                   # Delete closed >30 days ago
-bd cleanup --dry-run --json                                 # Preview what would be deleted
-bd cleanup --older-than 90 --cascade --force --json         # Delete old + dependents
+bd admin cleanup --force --json                                   # Delete ALL closed issues
+bd admin cleanup --older-than 30 --force --json                   # Delete closed >30 days ago
+bd admin cleanup --dry-run --json                                 # Preview what would be deleted
+bd admin cleanup --older-than 90 --cascade --force --json         # Delete old + dependents
 ```
 
 ### Duplicate Detection & Merging
@@ -319,15 +319,15 @@ bd merge bd-42 bd-43 --into bd-41 --dry-run            # Preview merge
 
 ```bash
 # Agent-driven compaction
-bd compact --analyze --json                           # Get candidates for review
-bd compact --analyze --tier 1 --limit 10 --json       # Limited batch
-bd compact --apply --id bd-42 --summary summary.txt   # Apply compaction
-bd compact --apply --id bd-42 --summary - < summary.txt  # From stdin
-bd compact --stats --json                             # Show statistics
+bd admin compact --analyze --json                           # Get candidates for review
+bd admin compact --analyze --tier 1 --limit 10 --json       # Limited batch
+bd admin compact --apply --id bd-42 --summary summary.txt   # Apply compaction
+bd admin compact --apply --id bd-42 --summary - < summary.txt  # From stdin
+bd admin compact --stats --json                             # Show statistics
 
 # Legacy AI-powered compaction (requires ANTHROPIC_API_KEY)
-bd compact --auto --dry-run --all                     # Preview
-bd compact --auto --all --tier 1                      # Auto-compact tier 1
+bd admin compact --auto --dry-run --all                     # Preview
+bd admin compact --auto --all --tier 1                      # Auto-compact tier 1
 
 # Restore compacted issue from git history
 bd restore <id>  # View full history at time of compaction

docs/CONFIG.md

@@ -576,7 +576,7 @@ jira_project = get_config("jira.project")
 
 Some bd commands automatically use configuration:
 
-- `bd compact` uses `compact_tier1_days`, `compact_tier1_dep_levels`, etc.
+- `bd admin compact` uses `compact_tier1_days`, `compact_tier1_dep_levels`, etc.
 - `bd init` sets `issue_prefix`
 
 External integration scripts can read configuration to sync with Jira, Linear, GitHub, etc.

docs/DELETIONS.md

@@ -66,7 +66,7 @@ Tombstones expire after a configurable TTL (default: 30 days). This prevents unb
 ### How Expiration Works
 
 1. Tombstones older than TTL + 1 hour grace period are eligible for pruning
-2. `bd compact` removes expired tombstones from `issues.jsonl`
+2. `bd admin compact` removes expired tombstones from `issues.jsonl`
 3. Git history fallback handles edge cases where pruned tombstones are needed
 
 ### Configuration
@@ -85,7 +85,7 @@ bd config set tombstone.ttl_days 60
 ### Manual Pruning
 
 ```bash
-bd compact                         # Prune expired tombstones (and other compaction)
+bd admin compact                   # Prune expired tombstones (and other compaction)
 ```
 
 ## Conflict Resolution
@@ -163,7 +163,7 @@ If you have many old tombstones:
 bd list --status=tombstone | wc -l
 
 # Prune expired tombstones
-bd compact
+bd admin compact
 ```
 
 ## Design Rationale

docs/FAQ.md

@@ -333,10 +333,10 @@ Use compaction to remove old closed issues:
 
 ```bash
 # Preview what would be compacted
-bd compact --dry-run --all
+bd admin compact --dry-run --all
 
 # Compact issues closed more than 90 days ago
-bd compact --days 90
+bd admin compact --days 90
 ```
 
 Or split your project into multiple databases:

docs/QUICKSTART.md

@@ -178,16 +178,16 @@ As your project accumulates closed issues, the database grows. Manage size with
 
 ```bash
 # View compaction statistics
-bd compact --stats
+bd admin compact --stats
 
 # Preview compaction candidates (30+ days closed)
-bd compact --analyze --json --no-daemon
+bd admin compact --analyze --json --no-daemon
 
 # Apply agent-generated summary
-bd compact --apply --id bd-42 --summary summary.txt --no-daemon
+bd admin compact --apply --id bd-42 --summary summary.txt --no-daemon
 
 # Immediately delete closed issues (CAUTION: permanent!)
-bd cleanup --force
+bd admin cleanup --force
 ```
 
 **When to compact:**

docs/TROUBLESHOOTING.md

@@ -486,10 +486,10 @@ Check database size and consider compaction:
 bd stats
 
 # Preview compaction candidates
-bd compact --dry-run --all
+bd admin compact --dry-run --all
 
 # Compact old closed issues
-bd compact --days 90
+bd admin compact --days 90
 ```
 
 ### Large JSONL files
@@ -501,7 +501,7 @@ If `.beads/issues.jsonl` is very large:
 ls -lh .beads/issues.jsonl
 
 # Remove old closed issues
-bd compact --days 90
+bd admin compact --days 90
 
 # Or split into multiple projects
 cd ~/project/component1 && bd init --prefix comp1