model_specs: fix declarations that accept or reject the wrong requests

[CryptVenture]

Split out of #372 as requested. This PR holds only the changes that alter which requests validate; the description-only fixes, the VoxCPM1 defaults, the ASR/aligner/codec declarations and the MiniMax declarations are separate PRs.

Each change is listed with the exact parser that reads the option.

The changes

midashenglm_gen.seed: min -1 → 0. src/models/midashenglm_gen/session.cpp:176 reads the seed through runtime::parse_u32_option, and parse_u32_value (src/framework/runtime/options.cpp:36-39) throws "seed must be an unsigned integer" on any leading minus. A spec-legal -1 was therefore a guaranteed runtime error, and the "-1 selects a random seed" description promised behaviour that could not happen.

heartmula.lyrics, heartmula.tags: required false → true. src/models/heartmula/session.cpp throws "HeartMuLa requires non-empty tags" and "HeartMuLa requires non-empty lyrics". The engine already rejected what the spec described as valid, so a client could not learn the constraint until the request failed.

irodori_tts.text_chunk_mode: default and tag_aware added to the enum. The session takes the shared override (src/models/irodori_tts/session.cpp:453-454 → text::parse_text_chunk_mode_override), and src/framework/text/chunking.cpp:572-586 accepts default, word_budget, tag_aware, japanese, endline. Two working modes were undeclared and so unreachable from a spec-driven client.

granite5asr.language: removed. The session never reads a language option — it hard-codes "en" (src/community_models/granite5asr/session.cpp:137, 174, 252, 270, 277). The declaration invited a value that could not have an effect.

firered_audio session option helper_graph_arena_mb: removed. The only key that exists is fireredtts3.helper_graph_arena_mb (src/models/fireredtts3/session.cpp:251). FireRedAudio validates session options strictly, so sending the declared name failed the request outright.

Validation

python3 tools/check_loader_catalog_sync.py
# ok: runtime loaders, model_specs, and model_manager_v2 are in sync

audiocpp_model_manager list --repository-root .        # exit 0
# parses every on-disk spec through the C++ schema loader

Verified by reading the parser that consumes each option, with the file and line above. None of these five families has a package installed on this machine, so they were not exercised end to end; the sibling ASR PR carries a live request check for the one family that is installed here.

Scope

Five spec files, 6 insertions / 19 deletions. The generated WebUI bundle is deliberately excluded: catalog.ts inlines model_specs/*.json at frontend build time and the bundle is not byte-reproducible, so regenerating it in every PR of this split would make the PRs conflict with each other. 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.