refactor(core)!: rename Provider to LLMProvider and update implementations

- Export `LLMProvider` from `owlen-core` and replace public `Provider` re-exports.
- Convert `OllamaProvider` to implement the new `LLMProvider` trait with associated future types.
- Adjust imports and trait bounds in `remote_client.rs` to use the updated types.
- Add comprehensive provider interface tests (`provider_interface.rs`) verifying router routing and provider registry model listing with `MockProvider`.
- Align dependency versions across workspace crates by switching to workspace-managed versions.
- Extend CI (`.woodpecker.yml`) with a dedicated test step and generate coverage reports.
- Update architecture documentation to reflect the new provider abstraction.

.woodpecker.yml

@@ -39,6 +39,14 @@ matrix:
       EXT: ".exe"
 
 steps:
+  - name: tests
+    image: *rust_image
+    commands:
+      - rustup component add llvm-tools-preview
+      - cargo install cargo-llvm-cov --locked
+      - cargo llvm-cov --workspace --all-features --summary-only
+      - cargo llvm-cov --workspace --all-features --lcov --output-path coverage.lcov --no-run
+
   - name: build
     image: *rust_image
     commands: