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

CHANGELOG.md

@@ -148,3 +148,31 @@
 
 ### Models Updated
 - `AppConfig`: added `EncryptionEnabled`, `PasswordHash`, `KnownHostsFile`
+
+## Phase 2 UX Polish (Done)
+
+### Theme System
+- **NEW `themes.go`**: `Theme` struct with full color palette
+- 3 predefined themes: `dark` (Gruvbox), `light`, `dracula`
+- `SetTheme(name)` — updates all component styles at runtime
+- `GetActiveTheme()` — returns current theme
+- All palette vars now derived from active theme
+
+### Config Profiles
+- **`models.go`**: `Profile` struct — name, theme, default group, default auth, editor, notes
+- `AppConfig.Profiles []Profile` — list of named profiles
+- `AppConfig.ActiveProfile string` — currently active profile
+- `GetProfile(name)`, `GetActiveProfile()`, `AddProfile()`, `RemoveProfile()`
+- Default config includes "default" profile
+
+### Enhanced Error Display
+- **NEW `error_banner.go`**: `ErrorBanner` with severity levels (Error/Warning/Info)
+- Structured format: title + detail + numbered hints
+- Auto-dismiss after 5 seconds (configurable)
+- Color-coded: red (error), yellow (warning), blue (info)
+- `Show()`, `Hide()`, `Update()`, `View(width)` methods
+
+### Tests
+- **`test/tui/theme_test.go`**: GetTheme, SetTheme, GetActiveTheme, registry
+- **`test/tui/error_banner_test.go`**: Show/Hide, AutoDismiss, Severity, View
+- **`test/models_test.go`**: DefaultConfig, Profile CRUD