feat(gallery): add all Italian + all UK English sherpa-onnx Piper voices (#10332)

Expands sherpa-onnx Piper TTS coverage in the model gallery. Previously only
5 single-speaker Piper voices shipped (it_IT-paola, en_US-amy, es_ES-davefx,
fr_FR-siwis, de_DE-thorsten). This adds 19 entries:

Italian (it_IT): dii-high, miro-high, riccardo-x_low.
UK English (en_GB): alan (low+medium), alba-medium, aru-medium, cori
(high+medium), dii-high, jenny_dioco-medium, miro-high,
northern_english_male-medium, semaine-medium, southern_english_female
(low+medium), southern_english_male-medium, vctk-medium, sweetbbak-amy.

Each entry mirrors the existing Piper block (sherpa-onnx-tts.yaml base config).
sha256, ONNX path, sample rate and speaker count were read from the actual
release tarballs; licenses and source URLs were taken from each archive's
MODEL_CARD/README rather than assumed:

- dii/miro voices are OpenVoiceOS models under CC BY-NC-SA 4.0 (non-commercial),
  labelled as such in both the license field and description.
- cori is LibriVox public-domain (cc0-1.0); OpenSLR-83 voices are CC BY-SA 4.0;
  alba/vctk are CC BY 4.0.
- vctk (109), aru (12) and semaine (4) are multi-speaker; tagged accordingly
  with a note to select the speaker via the numeric voice id.

The legacy underscore-named southern_english_female_medium duplicate is
intentionally skipped. No backend change is needed: sherpa-onnx auto-detects
single-speaker VITS vs Kokoro, and each tarball ships its own espeak-ng-data.


Assisted-by: Claude:claude-opus-4-8 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

Author: localai-bot