fix(routing): offered tools must not make a local model unroutable

Verified against a real Open WebUI container: it attaches its ~26 built-in
tools (knowledge bases, notes, calendar, ...) to every single message, and
resolve() treated that offer as a hard capability requirement. On a pool of
tools-less local models a plain "hello" therefore failed with "No healthy
model available that satisfies required capabilities", and a pinned local
model was reported as "not available - not in the pool (deleted?)".

In the OpenAI contract `tools` is an offer; only tool_choice: "required" (or
a named function) makes the call impossible without them. Keep preferring a
tool-capable model, but fall back to serving the request with the tools
stripped - together with tool_choice/parallel_tool_calls, which a provider
rejects on their own. A pin whose only shortcoming is tool support is now
honoured; an unknown pin and tool_choice: "required" still fail loudly.

The downgrade is never silent: X-Cortiq-Tools-Dropped: true, plus
cortiq.tools_dropped in the echo block.

CHANGELOG.md

@@ -3,6 +3,27 @@
 All notable changes to this project are documented here.
 The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
+## [0.2.46] - 2026-08-21
+
+Verified end to end against a real Open WebUI container talking to the gateway.
+
+### Fixed
+- **Offered `tools` no longer make a local model unroutable.** Open WebUI attaches its ~26
+  built-in tools (knowledge bases, notes, calendar, …) to *every* message, and the gateway
+  treated that offer as a hard capability requirement — so a plain "hello" against a pool of
+  tools-less local models failed with «No healthy model available that satisfies required
+  capabilities». In the OpenAI contract `tools` is an offer: only `tool_choice: "required"`
+  (or a named function) makes the call impossible without them. The gateway now still
+  prefers a tool-capable model, but falls back to serving the request with the tools
+  stripped (along with `tool_choice`/`parallel_tool_calls`, which a provider rejects on
+  their own). `tool_choice: "required"` still fails loudly, as it must.
+- **A pinned model that merely lacks tool support is honoured** instead of being reported as
+  «not available — it is not in the pool (deleted?)». An unknown pin still fails loudly.
+
+### Added
+- `X-Cortiq-Tools-Dropped: true` (and `cortiq.tools_dropped` in the echo block) whenever the
+  gateway answers without the tools the client offered, so the downgrade is never silent.
+
 ## [0.2.45] - 2026-08-21
 
 ### Fixed