fix(models): deepseek-flash in the offline catalog and the pinned expectations

CI on 10aa19570 failed three suites on the new DeepSeek default: the agent
registry test (fixed by 5ad9cdbbd), config::model_completion_scenario still
pinned the pre-V4.1 list, and the subagent catalog-facade guard failed
because the offline models_dev seed never gained the new id while
OFFICIAL_DEEPSEEK_MODELS had.

- models_dev.bundled.json: add the `deepseek-flash` row (V4.1 Flash,
  text-only, 1M/384K, reasoning, tool_call) and move the provider
  `default: true` flag to it, matching the file own default_rows invariant
  (default equals DEFAULT_DEEPSEEK_MODEL, which is deepseek-flash).
- config/tests.rs: completion list expectation includes deepseek-flash.

Evidence:
- cargo test -p codewhale-tui --lib --locked -- config::tests::model_completion_scenario
  test result: ok. 2 passed; 0 failed
- ... -- operator_model_for_subagent_enumerates_from_catalog_facade
  test result: ok. 1 passed; 0 failed (was FAILED: facade dropped deepseek-flash)
- cargo test -p codewhale-config --locked -- models_dev
  test result: ok. 26 passed; 0 failed
- cargo test -p codewhale-tui --lib --locked -- provider_lake
  test result: ok. 34 passed; 0 failed

crates/tui/src/config/tests.rs

@@ -7494,6 +7494,7 @@ fn model_completion_scenario() {
             model_completion_names_for_provider(ApiProvider::Deepseek),
             vec![
                 "deepseek-v4-pro",
+                "deepseek-flash",
                 "deepseek-v4-flash",
                 "deepseek-v4-flash-vision-exp"
             ]