add tool plugin param type date and date-picker

[zyqzyq]

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Fixes #36162

Summary

This change adds first-class support for date and date-picker tool/plugin parameter types end to end: schema normalization, backend typing/casting, workflow UI (tool node, variable picker, constant field, trigger form), plugin reasoning configuration, and i18n. Values for date are handled as a single calendar day (string); date-picker represents an optional start/end range serialized as a JSON string/object consistent with backend casting.

Backend

• Extended CommonParameterType with DATE and DATE_PICKER (api/core/entities/parameter_entities.py).
• Wired PluginParameterType / ToolParameterType and cast_parameter_value / as_normal_type logic for date and date-picker (api/core/plugin/entities/parameters.py, api/core/tools/entities/tool_entities.py).
• Added unit coverage for enum values and date-picker casting edge cases (api/tests/unit_tests/core/entities/test_entities_parameter_entities.py).

Frontend

• Added FormTypeEnum.date and FormTypeEnum.datePicker (declarations.ts) and schema mapping in to-form-schema.ts (including aliases such as datepicker → date-picker).
• Centralized declarative type matching via toolDeclarativeTypeMatches in form-input-item.helpers.ts (used by form input, variable picker, reasoning config, and input variable list).
• Tool / trigger forms: form-input-item.tsx renders a native date input for date and ToolDateRangePicker for date-picker (timezone from app context). constant-field.tsx, input-var-list.tsx, tool-form/item.tsx, and trigger-plugin/.../trigger-form/item.tsx updated for labels, tooltips, and picker behavior.
• Variable reference UX: var-reference-picker.tsx / var-reference-picker.trigger.tsx force constant mode for date-picker and hide the mixed constant/variable type switch where inappropriate.
• Plugin reasoning panel: reasoning-config-form.tsx + reasoning-config-form.helpers.ts aligned with the same types, filters, and ToolDateRangePicker.
• New UI pieces: tool-date-range-picker.tsx, tool-date-range-value.ts (parse/stringify range payload); cn from @langgenius/dify-ui/cn for bundler compatibility.
• i18n: nodes.tool.dateRange.* in web/i18n/en-US/workflow.json and web/i18n/zh-Hans/workflow.json.
• Tests: form-input-item.helpers.spec.ts, reasoning-config-form.helpers.spec.ts for declarative matching and date / date-picker behavior.

Screenshots

Before	After
Tool parameters typed as date / date-picker in provider YAML were not rendered with dedicated controls in the workflow tool node and related pickers.	Native date control and start/end range picker for date-picker, with correct variable filtering and constant-only behavior where required.

(Replace the table cells with embedded images if you attach screenshots in the PR.)

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods