fix(models): four provider-catalog and connection defects (#3262, #3115, #3486, #3467) - #3880

…olua#3486)

Individual models carry context_length and max_completion_tokens; combo
entries were built as bare { id, object, owned_by } and skipped them. A
client that sizes its context window off /v1/models therefore fell back to
guessing from the model name, and guessed against a pool whose members can
be far wider - a 1M pool read as deepseek 128k, compacting at ~96k.

Emit the same two snake_case fields on combo entries. A request routed to
a combo can land on any member, so the pool can only promise what its
smallest member accepts: take the minimum across members.

A member that reports no usable number is skipped rather than read as
zero, and when no member reports one the field is omitted entirely - an
absent field lets the client fall back, a wrong one does not.

Web-search and web-fetch combos are untouched: they are not chat models
and carry no window.

The alias-to-provider map the DB-unavailable branch already built is
hoisted so the combo loop can share it, rather than building a second.

…ecolua#3467)

The three self-hosted providers read their endpoint from
providerSpecificData.baseUrl, and their own registry entries tell the user
to set it:

    text: "Set providerSpecificData.baseUrl to the server root, e.g.
           http://host:8080 — /v1/audio/speech is appended."

The dashboard never rendered a field for it. Every connection created
through the UI was therefore saved without one and fell back to the
built-in localhost default — which inside Docker is the 9router container
itself, so a separately hosted server is unreachable and nothing says why.

The modal did have such a field, but it was hardcoded to one provider:

    const isOllamaLocal = provider === "ollama-local";
    {isOllamaLocal && <Input label="Ollama Host URL" ... />}

Make it declarative instead. A provider whose endpoint is per-connection
now says so in its registry entry:

    baseUrlField: { label, placeholder, help }

and the modal renders whatever the registry declares. ollama-local moves
onto the same mechanism rather than keeping a second one beside it, with
its label and placeholder preserved exactly.

The placeholders are each provider's real fallback, so the box shows what
the connection would otherwise use.

buildProviderSpecificData moves into src/shared/utils so the saved shape
can be tested without rendering. An empty box still saves nothing: it
means "keep the default", not "save an empty endpoint".