* perf: cache KaTeX module import as singleton across all renderer instances
KatexRenderer.svelte dynamically imports katex, mhchem, and the CSS on every component mount. When a message contains multiple math expressions, this triggers redundant module resolution for each one. Move the import promise to a module-level singleton using Svelte's context='module' script block so it loads once and is shared across all KatexRenderer instances.
* Update KatexRenderer.svelte
ResponseMessage compared the entire message object via JSON.stringify on every reactive tick to detect changes. During streaming, content changes on every token, making the two O(content_length) JSON.stringify calls always return different results — pure wasted work. Add a fast O(1) comparison on content and done fields first. When either differs (the common streaming case), skip straight to cloning. Only fall through to the expensive JSON.stringify comparison for infrequent changes like sources, annotations, or status updates.
fix: model fallback routing for all model types and default model selection
Backend: When ENABLE_CUSTOM_MODEL_FALLBACK is active and a custom model's
base model is unavailable, the fallback now swaps the model and form data
to the configured default model directly. This ensures routing uses the
fallback model's type (pipe, Ollama, or OpenAI) instead of the original
model's type, which previously caused "Model not found" errors when the
fallback was a different backend type.
Frontend: Fixed default model selection in new chat initialization where
the admin-configured default models were always overwritten by the first
available model. The first-available fallback now only triggers when the
configured defaults don't resolve to valid available models.
This commit adds aria-labels to the text inputs and textareas that previously lacked them, applies role=switch to inputs, and adds accessible titles to floating quick actions.
