feat: count chip inside multi-select filter input (PIN-9840)

[Alepazz]

🔗 Issue

PIN-9840 — [FND] - Componente AutoComplete

Note: this PR builds on top of PIN-7358 (filters redesign, branch feature/PIN-7358_filters-redesign). It should be reviewed and merged after PIN-7358 is finalized. See the Prerequisite section below.

📝 Description / Context

The current multi-select filter field (autocomplete-multiple) renders one removable Chip per selection both inside the input (making it grow vertically) and as a row of chips under the fields. This hurts accessibility and clashes with the new design direction.

This PR explores the feasibility of a redesign where multi-select fields stay compact, showing a single chip with the selection count inside the input itself (see mockup attached to the Jira ticket). After selecting options the user sees only the count + a close icon to clear all, not a wall of removable tags.

This PR is opened as draft to drive the discussion with the design team before finalizing pixel-level details.

🛠 List of changes

• AutocompleteMultipleFilterField: renders a count Chip with a close icon when ≥1 option is selected; onDelete clears all selections; stopPropagation avoids opening the dropdown.
• AutocompleteBaseFilterField: new internal endAdornmentExtra slot, prepended to MUI's default endAdornment when present. Excluded from the spread to <Autocomplete> so it never lands on the DOM.
• ActiveFiltersChips: multi-select filters no longer render as removable chips in the summary row (their selection is already shown inside the input). Other filter types (single-value, freetext, datepicker, numeric) still render as chips.
• Filters.test.tsx + snapshots updated to reflect the new rendering.

🧪 How to test

Link this branch into pdnd-interop-frontend (via pnpm link or file: protocol) — no consumer code change is required, the new behavior is the default for all autocomplete-multiple fields.

Suggested pages:

• Consumer → E-service catalog → "Erogato da" filter
• Provider → E-service list
• Any other page using type: 'autocomplete-multiple' in useFilters

Checklist:

• Select 1-N options: count chip appears and updates reactively
• Click the × on the count chip: all selections cleared, URL params updated
• The dropdown does NOT open when clicking the ×
• Reload with selections already in URL: count chip reflects the correct count on mount
• The summary chip row below no longer duplicates multi-select chips
• Single-select filters (e.g. Notifiche → read/unread) remain unchanged
• "Annulla filtri" button still clears multi-select too

⚠️ Open points to discuss before "Ready for review"

• Rollout strategy: evaluate whether we should introduce an opt-in flag (variant: 'chips' | 'count-chip') to stagger the migration, or proceed with this breaking change as-is. Current implementation takes the second path for simplicity.
• Design review: confirm chip color, size, spacing, close icon, focus/hover states with design against the Jira mockup. Implementation uses placeholder values (color="primary", size="small").
• Consumer migration: list and QA every page in pdnd-interop-frontend (and any other commons consumer) declaring an autocomplete-multiple filter. No API change required, visual regression testing advisable.
• Versioning: breaking visual change — agree on semver bump. Natural choice is a major release (1.x.x → 2.0.0); alternatively a minor with the opt-in flag mentioned above.
• Accessibility: the Jira ticket mentions the current component is not fully accessible. Verify aria-label on the clear chip, keyboard navigation (Escape closes dropdown, Backspace does not remove selections), visible focus ring in the filled state, screen-reader announcement of the count.

📎 Prerequisite

This PR is a follow-up / evolution of PIN-7358 (branch feature/PIN-7358_filters-redesign). Merge order should be:

1. PIN-7358 gets reviewed, the filter-applied issues already flagged there get addressed, then merged into develop.
2. This branch gets rebased on top of the updated develop.
3. Any interaction between hasSubmitButton (introduced by PIN-7358) and the count-chip UX introduced here is resolved during the rebase.

🖼️ Pictures