refactor(store,tools): migrate IDs from UUID to bigserial int64

All internal entity lookups now use bigserial primary keys (int64) while
GUIDs are retained for external/public identification. Updated store
functions (TouchProject, UpdateThoughtMetadata, AddThoughtAttachment) to
query by id instead of guid, added GetThoughtByID, changed semanticSearch
and all tool helpers to use *int64 project IDs, and updated retry/backfill
workers to use int64 thought IDs throughout.

internal/types/plan.go

@@ -27,18 +27,19 @@ const (
 )
 
 type Plan struct {
-	ID               uuid.UUID    `json:"id"`
+	ID               int64        `json:"id"`
+	GUID             uuid.UUID    `json:"guid"`
 	Title            string       `json:"title"`
 	Description      string       `json:"description"`
 	Status           PlanStatus   `json:"status"`
 	Priority         PlanPriority `json:"priority"`
-	ProjectID        *uuid.UUID   `json:"project_id,omitempty"`
+	ProjectID        *int64       `json:"project_id,omitempty"`
 	Owner            string       `json:"owner,omitempty"`
 	DueDate          *time.Time   `json:"due_date,omitempty"`
 	CompletedAt      *time.Time   `json:"completed_at,omitempty"`
 	ReviewedBy       string       `json:"reviewed_by,omitempty"`
 	LastReviewedAt   *time.Time   `json:"last_reviewed_at,omitempty"`
-	SupersedesPlanID *uuid.UUID   `json:"supersedes_plan_id,omitempty"`
+	SupersedesPlanID *int64       `json:"supersedes_plan_id,omitempty"`
 	Tags             []string     `json:"tags"`
 	CreatedAt        time.Time    `json:"created_at"`
 	UpdatedAt        time.Time    `json:"updated_at"`
@@ -56,7 +57,7 @@ type PlanDetail struct {
 
 type PlanFilter struct {
 	Limit     int
-	ProjectID *uuid.UUID
+	ProjectID *int64
 	Status    string
 	Priority  string
 	Owner     string
@@ -77,7 +78,7 @@ type PlanUpdate struct {
 	ClearCompletedAt      bool
 	ReviewedBy            *string // "" to clear
 	MarkReviewed          bool    // sets last_reviewed_at = now()
-	SupersedesPlanID      *uuid.UUID
+	SupersedesPlanID      *int64
 	ClearSupersedesPlanID bool
 	Tags                  *[]string // nil = no change; replace when non-nil
 }