feat(command-palette): add fuzzy model/provider filtering, expose ModelPaletteEntry, and show active model with provider in UI header

- Introduce `ModelPaletteEntry` and re‑export it for external use.
- Extend `CommandPalette` with dynamic sources (models, providers) and methods to refresh suggestions based on `:model` and `:provider` prefixes.
- Implement fuzzy matching via `match_score` and subsequence checks for richer suggestion ranking.
- Add `provider` command spec and completions.
- Update UI to display “Model (Provider)” in the header and use the new active model label helper.
- Wire catalog updates throughout `ChatApp` (model palette entries, command palette refresh on state changes, model picker integration).

crates/owlen-tui/src/state/mod.rs

@@ -7,4 +7,4 @@
 
 mod command_palette;
 
-pub use command_palette::CommandPalette;
+pub use command_palette::{CommandPalette, ModelPaletteEntry};