feat: support all existing bid modifiers

[Adel7418]

Summary

• add normalized GET /yandex/campaigns/{campaign_id}/bid-modifiers response for all bid modifier rows returned by Direct
• generalize POST /yandex/campaigns/{campaign_id}/bid-modifiers request model from age-only to existing modifier updates by modifier_id
• document/test safe weather modifier boundary: read existing weather modifier first, then update coefficient by Id; no create-new-weather-modifier behavior
• keep live apply payload minimal: {Id, BidModifier} only, with existing approval/idempotency/live_write gates

Safety

• No live Yandex writes performed
• No commit/push/deploy to production runtime beyond this feature branch/PR
• Existing DirectPilot human approval contract remains required for real applies

Verification

• uv run pytest -q tests/test_bid_modifiers_update.py tests/test_bid_modifiers_models.py → 18 passed
• uv run pytest -q → 596 passed
• uv run python scripts/check_openapi_sync.py → OpenAPI snapshot is in sync
• uv run python scripts/check_no_secrets_in_git.py → No obvious tracked secrets detected

Notes

• This PR is based on origin/master to avoid mixing unrelated sitelinks/UTM work from the local dirty checkout.
• Reviewer gate previously passed; non-blocking future improvements: make _safe_int more tolerant of signed/whitespace strings and extend modifier type inference if new Direct provider shapes appear.