fix(web): split model selection and settings actions

[lyzno1]

What changed

• split the shared model control into independent model selection and model settings actions
• open the model list from the primary trigger and current-model parameters from the settings trigger
• disable model settings when no model is selected or the control is read-only
• apply the same contract to the main LLM model parameter control and the general plugin model selector

Why

The controls were visually presented as split buttons, but one popover trigger wrapped both regions. As a result, clicking either side opened model settings and the primary model-selection action was unavailable.

Impact

Default callers now get consistent split-button behavior from the shared owners without call-site wiring. Custom combined triggers and agent strategy triggers keep their existing behavior.

Validation

• pnpm -C web test app/components/header/account-setting/model-provider-page/model-parameter-modal/__tests__/index.spec.tsx app/components/plugins/plugin-detail-panel/model-selector/__tests__/index.spec.tsx app/components/workflow/nodes/llm/__tests__/panel.spec.tsx app/components/header/account-setting/model-provider-page/model-selector/__tests__/index.spec.tsx --run --reporter=dot
• pnpm -C web type-check
• git diff --check

Refs SNP-530

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.46%. Comparing base (6e5ba18) to head (658b400).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #38797      +/-   ##
==========================================
- Coverage   85.47%   85.46%   -0.01%     
==========================================
  Files        5025     5023       -2     
  Lines      273457   273438      -19     
  Branches    51259    51255       -4     
==========================================
- Hits       233729   233707      -22     
- Misses      35238    35241       +3     
  Partials     4490     4490              

Flag	Coverage Δ
dify-ui	94.61% <ø> (ø)
web	85.14% <100.00%> (-0.01%)	⬇️

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