feat(cards): add 'note' card type for readable markdown content

New card type renders body as styled markdown with no copy/fill/run
affordance. Glyph: ¶, color: --note.

Migration uses transaction to safely rebuild table constraint.
Checks both 'note' presence and modified_at column to catch
partial migration state.

internal/db/db.go

@@ -3,8 +3,10 @@ package db
 import (
 	"database/sql"
 	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	_ "modernc.org/sqlite"
 )
@@ -63,7 +65,7 @@ func (s *Store) migrate() error {
 			pinned      INTEGER NOT NULL DEFAULT 0,
 			deleted_at  TEXT,
 			card_type   TEXT
-				CHECK (card_type IN ('snippet', 'template', 'checklist', 'decision', 'link')
+				CHECK (card_type IN ('snippet', 'template', 'checklist', 'decision', 'link', 'note')
 				       OR card_type IS NULL),
 			card_data   TEXT,
 			use_count   INTEGER NOT NULL DEFAULT 0,
@@ -91,6 +93,58 @@ func (s *Store) migrate() error {
 	s.db.Exec(`ALTER TABLE entities ADD COLUMN title TEXT`)
 	s.db.Exec(`ALTER TABLE entities ADD COLUMN description TEXT`)
 
+	// Migrate CHECK constraint to include 'note' card type
+	var needsMigrate bool
+	row := s.db.QueryRow(`SELECT sql FROM sqlite_master WHERE type='table' AND name='entities'`)
+	var ddl string
+	if row.Scan(&ddl) == nil {
+		hasNote := strings.Contains(ddl, "'link', 'note'")
+		hasModified := strings.Contains(ddl, "modified_at")
+		needsMigrate = !hasNote || !hasModified
+	}
+	if needsMigrate {
+		tx, err := s.db.Begin()
+		if err != nil {
+			return err
+		}
+		defer tx.Rollback()
+
+		if _, err := tx.Exec(`ALTER TABLE entities RENAME TO _entities_migrate`); err != nil {
+			return fmt.Errorf("migrate rename: %w", err)
+		}
+		if _, err := tx.Exec(`CREATE TABLE entities (
+			id          TEXT PRIMARY KEY,
+			created_at  TEXT NOT NULL,
+			modified_at TEXT NOT NULL,
+			body        TEXT NOT NULL,
+			glyph       TEXT NOT NULL
+				CHECK (glyph IN ('todo', 'event', 'note')),
+			time_anchor TEXT,
+			completed_at TEXT,
+			pinned      INTEGER NOT NULL DEFAULT 0,
+			deleted_at  TEXT,
+			card_type   TEXT
+				CHECK (card_type IN ('snippet', 'template', 'checklist', 'decision', 'link', 'note')
+				       OR card_type IS NULL),
+			card_data   TEXT,
+			use_count   INTEGER NOT NULL DEFAULT 0,
+			last_used_at TEXT,
+			title       TEXT,
+			description TEXT
+		)`); err != nil {
+			return fmt.Errorf("migrate create: %w", err)
+		}
+		if _, err := tx.Exec(`INSERT INTO entities SELECT * FROM _entities_migrate`); err != nil {
+			return fmt.Errorf("migrate copy: %w", err)
+		}
+		if _, err := tx.Exec(`DROP TABLE _entities_migrate`); err != nil {
+			return fmt.Errorf("migrate drop: %w", err)
+		}
+		if err := tx.Commit(); err != nil {
+			return fmt.Errorf("migrate commit: %w", err)
+		}
+	}
+
 	return nil
 }
 

internal/db/entities.go

@@ -27,6 +27,7 @@ const (
 	CardChecklist CardType = "checklist"
 	CardDecision  CardType = "decision"
 	CardLink      CardType = "link"
+	CardNote      CardType = "note"
 )
 
 func ValidGlyph(s string) bool {
@@ -39,7 +40,7 @@ func ValidGlyph(s string) bool {
 
 func ValidCardType(s string) bool {
 	switch CardType(s) {
-	case CardSnippet, CardTemplate, CardChecklist, CardDecision, CardLink:
+	case CardSnippet, CardTemplate, CardChecklist, CardDecision, CardLink, CardNote:
 		return true
 	}
 	return false