feat(custom-model): estimate model load time from its discovered size

Discovery now also parses a GB figure out of an auto-discovered model's own
description (llama-swap writes "Auto-discovered 16.35 GB - parameters
auto-fitted by llama.cpp"), stored per model as modelSizesGB - unlike
context length this needs no /props probe (the figure is right there in
/v1/models) so it is populated for every model regardless of loaded state.
A hand-configured profile's own description has no such figure and
correctly gets no entry.

The loading banner (_watchLlamaSwapLoading) now looks this up and, when
known, shows it plus a rough estimate from a small size->time matrix
(_estimateModelLoad/_MODEL_LOAD_TIME_MATRIX, session-ui.js) -
"Loading qwen3.8-27b-ud-q4_k_xl (16.4 GB, typically ~1-3 min) on
llama-swap... this can take a while" - and uses that same estimate's own
bracket to scale the banner's default give-up timeout for a very large
model, instead of a flat 5 minutes for everything. Explicitly labelled as
an UNMEASURED, typical-hardware estimate in every relevant comment - this
is not benchmarked against any real endpoint's actual storage/GPU, just a
reasonable expectation-setter. A model with no discoverable size (a
hand-configured profile) gets no size/estimate shown at all, matching the
"never a guess" convention modelContextLengths already established.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqZeHrRS6DYcGcGX2p9EwG

src/web/schemas.ts

@@ -1946,6 +1946,8 @@ export const CustomModelHostSchema = z.object({
   // Server-populated by discovery (custom-model-routes.ts); accepted here only so a client
   // round-tripping the GET response back through PUT (edit-save) doesn't drop it.
   modelContextLengths: z.record(z.string().max(200), z.number().int().positive().max(100_000_000)).optional(),
+  // Same reasoning as modelContextLengths above.
+  modelSizesGB: z.record(z.string().max(200), z.number().positive().max(100_000)).optional(),
 });
 
 /** POST /api/sessions/:id/custom-model — apply or clear a session's custom-model selection. */