feat: Phase 2 UX Polish — theme system, config profiles, error banner, tests

- Add Theme struct with 3 predefined themes (dark/light/druntime)
- Add Profile struct for named configuration profiles
- Add ErrorBanner with severity levels and auto-dismiss
- Add unit tests for theme, error banner, and models
- Update CHANGELOG.md and PROJECT_STATE.md

internal/models/models.go

@@ -50,6 +50,16 @@ type Snippet struct {
 	UpdatedAt time.Time `json:"updated_at"`
 }
 
+// Profile represents a named configuration profile
+type Profile struct {
+	Name         string `json:"name"`
+	Theme        string `json:"theme"`
+	DefaultGroup string `json:"default_group,omitempty"`
+	DefaultAuth  string `json:"default_auth,omitempty"` // "password", "key", "both"
+	Editor       string `json:"editor,omitempty"`
+	Notes        string `json:"notes,omitempty"`
+}
+
 // AppConfig represents the application configuration
 type AppConfig struct {
 	Version           string `json:"version"`
@@ -60,6 +70,10 @@ type AppConfig struct {
 	AutoSync          bool   `json:"auto_sync"`
 	SyncProvider      string `json:"sync_provider,omitempty"`
 
+	// Profiles
+	Profiles      []Profile `json:"profiles,omitempty"`
+	ActiveProfile string    `json:"active_profile,omitempty"`
+
 	// Security
 	EncryptionEnabled bool   `json:"encryption_enabled"`
 	PasswordHash      string `json:"password_hash,omitempty"` // SHA-256 hash for verification
@@ -68,10 +82,10 @@ type AppConfig struct {
 
 // KnownHost represents a verified host key
 type KnownHost struct {
-	Hostname string `json:"hostname"`
-	Port     int    `json:"port"`
-	KeyType  string `json:"key_type"`  // "ssh-rsa", "ssh-ed25519", etc.
-	KeyHash  string `json:"key_hash"`  // Base64-encoded host key
+	Hostname string    `json:"hostname"`
+	Port     int       `json:"port"`
+	KeyType  string    `json:"key_type"`  // "ssh-rsa", "ssh-ed25519", etc.
+	KeyHash  string    `json:"key_hash"`  // Base64-encoded host key
 	AddedAt  time.Time `json:"added_at"`
 }
 
@@ -85,5 +99,42 @@ func DefaultConfig() *AppConfig {
 		Editor:            "vim",
 		AutoSync:          false,
 		EncryptionEnabled: false,
+		Profiles: []Profile{
+			{
+				Name:  "default",
+				Theme: "dark",
+			},
+		},
+		ActiveProfile: "default",
+	}
+}
+
+// GetProfile returns a profile by name
+func (c *AppConfig) GetProfile(name string) *Profile {
+	for i := range c.Profiles {
+		if c.Profiles[i].Name == name {
+			return &c.Profiles[i]
+		}
+	}
+	return nil
+}
+
+// GetActiveProfile returns the active profile
+func (c *AppConfig) GetActiveProfile() *Profile {
+	return c.GetProfile(c.ActiveProfile)
+}
+
+// AddProfile adds a new profile
+func (c *AppConfig) AddProfile(p Profile) {
+	c.Profiles = append(c.Profiles, p)
+}
+
+// RemoveProfile removes a profile by name
+func (c *AppConfig) RemoveProfile(name string) {
+	for i := range c.Profiles {
+		if c.Profiles[i].Name == name {
+			c.Profiles = append(c.Profiles[:i], c.Profiles[i+1:]...)
+			return
+		}
 	}
 }