webui: drop parameter controls the engine never reads

[CryptVenture]

Split out of #374 as requested: controls the engine does not read. The default overrides, the range fixes, the missing groups and the label text are separate PRs.

Every control in model_params.json is sent with the request, so a control keyed to something the engine never reads is a widget that cannot do anything — and in three cases the working spelling was missing entirely.

Renamed to the key the engine actually reads

Group	Was	Now	Code
index_tts2	lang	language	src/models/index_tts2/request.cpp:90, session.cpp:370 read language; nothing reads lang
miotts	best_of_n	miotts.best_of_n	the prefixed key declared in src/models/miotts/loader.cpp:33
seed_vc	*_cfg_rate ×3	*_guidance_scale ×3	the old spellings survive only through the deprecation table in src/models/seed_vc/session.cpp:83-85

index_tts2 is the notable one: that is the multilingual selector, on the model whose headline feature is multilingual cloning, and it had never worked.

Removed

• ace_step's remix route and its five controls (source_caption, source_lyrics, flow_edit_n_min/max/avg). The engine defines its routes in src/models/ace_step/session.cpp and throws on anything else; remix appears nowhere in the tree.
• firered-audio-tts top_k, top_p, temperature. src/models/firered_audio/session.cpp:174-182 reads them while building the understanding request, never on the generation path this group drives.
• echo_tts seed. The server overwrites options["seed"] from the top-level field (app/server/runtime.cpp:1925), so the control could not take effect.

Validation

python3 -m json.tool webui/configs/model_params.json   # parses
python3 tools/check_loader_catalog_sync.py
# ok: runtime loaders, model_specs, and model_manager_v2 are in sync

Each claim above was checked against the file and line named beside it. The families with no package installed here were not run end to end.

Scope

One data file, 8 insertions / 17 deletions. No code change. The generated bundle is deliberately excluded — catalog.ts inlines this file at frontend build time and the bundle is not byte-reproducible, so regenerating it in each PR of this split would make the PRs conflict; happy to send one bundle-regeneration PR once the series lands.

[CryptVenture]

Closing for now to stay inside the 3-concurrent-PR policy (see the discussion on #422). Nothing is wrong with the change and CI is green on it; I will reopen it as review slots free.