[P1][LOCAL-02] Role-specific model packs

Programme: #1
Epic: #21

## Objective
Package local models by product role and measured hardware support instead of treating one large model as the answer to speech, retrieval, UI and coding.

## Scope
- Model-pack manifest: role, model/runtime IDs, hashes, tokenizer/templates, license, quantization, context limits, hardware requirements and evaluation results.
- Roles: coding/planning, fast extraction/UI planning, embeddings/reranking, speech-related support where applicable, and visual grounding.
- Signed downloads, resumable installation, disk management, rollback and version pinning.
- Disable loaders that execute untrusted repository/custom model code.
- Compatibility matrix per OS/accelerator/runtime.
- Benchmark/regression gate before default-pack promotion.

## Product rules
- Installed weights and active parameters are distinct concepts; publish realistic storage/RAM/VRAM requirements.
- Candidate model names are not permanent product promises.
- Privacy mode cannot change silently because a pack/runtime changes.

## Acceptance criteria
- [ ] Every installed pack exposes hashes, license, hardware/context limits and measured task results.
- [ ] Corrupt/unsigned/untrusted-code model packages are rejected.
- [ ] Rollback restores the last known-good compatible pack.
- [ ] Unsupported hardware receives a useful smaller-pack/degraded path rather than crash/OOM loops.
- [ ] Pack updates run regression suites before becoming defaults.
- [ ] Storage cleanup never deletes an actively required model without explicit state transition.

## Dependencies
- LOCAL-01
- SEC-03

**First phase:** P1
**Maturity target:** P5
**Owner:** local-ai-speech

No files, tests, or entry points are named. Start by reading dependencies LOCAL-01 and SEC-03, then break the scope into the manifest, package verification, rollback, hardware compatibility, storage state, and regression-gate requirements. Done means all listed acceptance criteria are met without unsafe packages, crashes on unsupported hardware, or silent privacy changes.

Written by the indexing model from the issue text.