Ati/cl 268 add date picker

[ati7697]

Summary

Adds a DatePicker component to Gooey — a single-component wrapper composing the existing Popover, Calendar, and Button primitives with a DateValue v-model. shadcn-vue does not ship a CLI-installable date picker; the upstream docs describe it as a documented composition, so this follows the SimpleSelect custom-wrapper pattern.

• src/components/date-picker/ — DatePicker.vue (composition + DateFormatter label, disabled prop, placeholder prop, locale prop defaulting to en-AU), index.ts, Cypress smoke spec
• app/pages/components/DatePicker.vue — showcase with Basic + Disabled examples
• Wired into src/index.ts, app/pages/index.ts, app/router/index.ts, and app/router/navigation.ts (sidebar — Forms group, between Checkbox and Field)
• Package bumped to 2.3.3 and dist/ rebuilt

Anything the reviewer needs to know

• No new runtime dependencies. @internationalized/date and lucide-vue-next are already pulled in by Calendar / used across the library.
• The component is filed alongside the shadcn block in src/index.ts but the route entry does not set shadcn: true (it's a custom composition, like SimpleSelect / ConfirmDialog).
• defineModel<DateValue>() is used for v-model — matches the type Calendar already accepts, so values flow through unchanged if you swap a bare Calendar for a DatePicker.
• No upstream shadcn primitives were modified.

Test plan

• npm run dev → visit /components/date-picker; click the trigger, pick a date, confirm the trigger label updates and the "Selected" line reflects the value
• Confirm "Date Picker" appears in the Forms sidebar group between Checkbox and Field
• npm run test (Cypress) — smoke spec passes
• npm run build succeeds

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