docs: add command palette, themes, sessions to Phase 2 roadmap

plan.md

@@ -163,7 +163,28 @@ CREATE TABLE context_state (
 - [x] Render final answer in normal assistant style (green/bold)
 - [x] Reasoning hidden by default, toggle with `tab` key
 - [x] Mouse support (`tea.WithMouseCellMotion()` + viewport scroll)
-- [ ] User-selectable themes (env var or file) for colors, reasoning style, input bar
+
+### Command Palette & Themes
+
+- [ ] `internal/channel/palette.go` — fuzzy-findable command palette overlay (Ctrl+P):
+  - Modal popup with search/filter input
+  - Renders a filtered list of commands with descriptions
+  - Enter to execute, Esc to dismiss
+- [ ] `/help` — show available commands with descriptions
+- [ ] `/new` — start a new conversation (alias: `/clear`)
+- [ ] `/exit` — quit the TUI (alias: `/quit`, `/q`)
+- [ ] `/thinking` — toggle visibility of reasoning/thinking blocks in the conversation
+- [ ] `/themes` — list and switch between color themes
+- [ ] `/sessions` — list and switch between conversations (alias: `/resume`)
+- [ ] `internal/channel/theme.go` — theme engine:
+  - JSON-based theme config with `defs` + `theme` color map
+  - Built-in themes: `default`, `tokyonight`, `catppuccin`, `gruvbox`, `nord`, `matrix`
+  - Uses `THEME` env var or `/themes` command to switch
+  - Hues: `primary`, `secondary`, `accent`, `text`, `textMuted`, `background`, `border`, `success`, `error`
+- [ ] `internal/channel/sessions.go` — session management:
+  - List existing conversations from SQLite
+  - Switch agent's active conversation
+  - Show per-session message count and last activity
 
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