Add RPC support for compact command (bd-184)

- Added OpCompact and OpCompactStats operation constants
- Added CompactArgs, CompactStatsArgs, and response types to RPC protocol
- Implemented handleCompact and handleCompactStats in RPC server
- Updated compact command to use RPC when daemon is available
- Fixed RPC client to include Cwd for proper database routing
- Compact now works in daemon mode with --no-daemon flag

Amp-Thread-ID: https://ampcode.com/threads/T-87885d07-80ad-466d-9ffb-cc96fab4853f
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/protocol.go

@@ -30,6 +30,8 @@ const (
 	OpReposReady      = "repos_ready"
 	OpReposStats      = "repos_stats"
 	OpReposClearCache = "repos_clear_cache"
+	OpCompact         = "compact"
+	OpCompactStats    = "compact_stats"
 )
 
 // Request represents an RPC request from client to daemon
@@ -230,3 +232,53 @@ type ReposStatsResponse struct {
 	PerRepo map[string]types.Statistics `json:"per_repo"`
 	Errors  map[string]string           `json:"errors,omitempty"`
 }
+
+// CompactArgs represents arguments for the compact operation
+type CompactArgs struct {
+	IssueID   string `json:"issue_id,omitempty"`   // Empty for --all
+	Tier      int    `json:"tier"`                 // 1 or 2
+	DryRun    bool   `json:"dry_run"`
+	Force     bool   `json:"force"`
+	All       bool   `json:"all"`
+	APIKey    string `json:"api_key,omitempty"`
+	Workers   int    `json:"workers,omitempty"`
+	BatchSize int    `json:"batch_size,omitempty"`
+}
+
+// CompactStatsArgs represents arguments for compact stats operation
+type CompactStatsArgs struct {
+	Tier int `json:"tier,omitempty"`
+}
+
+// CompactResponse represents the response from a compact operation
+type CompactResponse struct {
+	Success      bool              `json:"success"`
+	IssueID      string            `json:"issue_id,omitempty"`
+	Results      []CompactResult   `json:"results,omitempty"`     // For batch operations
+	Stats        *CompactStatsData `json:"stats,omitempty"`       // For stats operation
+	OriginalSize int               `json:"original_size,omitempty"`
+	CompactedSize int              `json:"compacted_size,omitempty"`
+	Reduction    string            `json:"reduction,omitempty"`
+	Duration     string            `json:"duration,omitempty"`
+	DryRun       bool              `json:"dry_run,omitempty"`
+}
+
+// CompactResult represents the result of compacting a single issue
+type CompactResult struct {
+	IssueID       string `json:"issue_id"`
+	Success       bool   `json:"success"`
+	Error         string `json:"error,omitempty"`
+	OriginalSize  int    `json:"original_size,omitempty"`
+	CompactedSize int    `json:"compacted_size,omitempty"`
+	Reduction     string `json:"reduction,omitempty"`
+}
+
+// CompactStatsData represents compaction statistics
+type CompactStatsData struct {
+	Tier1Candidates int     `json:"tier1_candidates"`
+	Tier2Candidates int     `json:"tier2_candidates"`
+	TotalClosed     int     `json:"total_closed"`
+	Tier1MinAge     string  `json:"tier1_min_age"`
+	Tier2MinAge     string  `json:"tier2_min_age"`
+	EstimatedSavings string `json:"estimated_savings,omitempty"`
+}