将 SAT 的 ES 召回与对外 size 解耦，并支持配置化（解决suggest接口size参数取值不同时返回结果不一致的问题）

**Problem**
When `size=10` vs `size=40`, the SAT (search‑as‑you‑type) ES `_search` used the same `size` value, causing different candidate pool sizes and inconsistent top‑N results after merging with completion suggestions. The `size` parameter incorrectly controlled three things: completion count, SAT ES `size`, and final truncation.

**Solution**
Introduce dedicated configurable bounds for SAT recall, completely decoupled from the client‑facing `size` (final result count).
- Compute SAT ES request size as `min(max(client_size, sat_recall_min), sat_recall_cap)`.
- Completion still uses the raw client `size`.
- Final merge, sort, and truncation logic (`_finalize_suggestion_list(..., size)`) unchanged.

**Configuration**
- New dataclass `SuggestionConfig` in `config/schema.py` with fields:
  - `sat_recall_min: int = 40`
  - `sat_recall_cap: int = 100`
- Root `config.yaml` now supports `suggestion.sat_recall_min` / `suggestion.sat_recall_cap`.
- Tenant overrides: `tenant_config.default.suggestion` or `tenant_config.tenants.<id>.suggestion` – only keys to override need to be specified. Merge order: root `SuggestionConfig` → default fragment → tenant fragment.
- Sanity check: if `sat_recall_cap < sat_recall_min`, both loader and runtime resolver raise `cap` to at least `min` (warning logged).

**Impact**
- Small `size` (e.g., 10) still gets a stable SAT candidate pool (minimum `sat_recall_min`).
- Large `size` is capped to `sat_recall_cap`, bounding ES query cost.
- Final result count remains exactly the HTTP `size` parameter.
- Backward compatible: defaults preserve previous behaviour when `sat_recall_min=40, sat_recall_cap=100` and client `size` <=100.

**Code changes**
- `config/schema.py`: add `SuggestionConfig` and integrate into `AppConfig`.
- `suggestion/service.py`:
  - `_resolve_suggestion_config_for_tenant()`: tenant‑aware config merging.
  - `SuggestionService._suggest()`: compute `sat_es_size` using the new bounds.
- `suggestion/loader.py`: apply same sanity checks and defaults.
- Tenant config example:
  ```yaml
  tenant_config:
    tenants:
      '163':
        suggestion:
          sat_recall_cap: 80
  ```

**Tests**
- `pytest tests/test_suggestions.py`
- `pytest tests/ci/test_service_api_contracts.py`
All related tests pass.