fix: cache_control ttl model check + batch create with explicit names

[koljahuang]

Summary

• Cache TTL fix: Only add ttl field to cache_control for Claude 4.5 family models (Opus 4.5, Sonnet 4.5, Haiku 4.5). Non-4.5 models like Sonnet 4 reject ttl with ValidationException: Extra inputs are not permitted. Also strips ttl from pre-existing client breakpoints on unsupported models.
• Batch token creation: Replace count + name_prefix (auto-generated prefix-001, prefix-002) with comma-separated names input. Frontend uses a textarea; backend auto-trims whitespace and ignores empty entries.

Changed files

File	Change
backend/app/services/bedrock.py	_model_supports_cache_ttl(), _new_cache_marker(), _inject_prompt_cache_breakpoints() accept model_id; _build_anthropic_body() passes model_id through
backend/app/api/admin/endpoints/tokens.py	BatchCreateTokenRequest: count+name_prefix → names (comma-separated string)
backend/app/services/token.py	create_tokens_batch(): count+name_prefix → names: List[str]
backend/tests/test_prompt_cache_injection.py	Updated for model-aware TTL; added supported/unsupported model tests
backend/tests/test_stream_failover.py	Mock signature fix for model_id param
frontend/src/stores/tokens.ts	BatchCreateTokenRequest interface updated
frontend/src/pages/TokensPage.vue	Batch dialog: textarea replaces prefix+count inputs

Test plan

• 27 prompt cache injection tests pass (including new TTL model checks)
• 65 total tests pass (excluding unrelated pricing test)
• Pre-commit hooks pass
• Verify Sonnet 4 + X-Bedrock-Auto-Cache: true + system prompt no longer returns Extra inputs are not permitted
• Verify Sonnet 4.5 still gets ttl: "1h" in cache_control
• Verify batch create with comma-separated names creates multiple tokens