feat(core): add payload rules, tag routing, and scheduled budgets

Introduce runtime-configurable payload mutation/filter rules with file
reload support and a settings API so upstream request bodies can be
customized per model and protocol without restarts.

Expand search support with Google PSE, Linkup, SearchAPI, and SearXNG,
including validation, routing, analytics costing, MCP schema updates,
and search-type-aware provider selection. Update Pollinations to support
anonymous access, endpoint failover, and the latest public model lineup.

Add OmniRoute response metadata headers/SSE comments, per-connection
model exclusion rules, combo tag-based routing, buffered spend writes,
and scheduled daily/weekly/monthly budget resets. Update model catalog
and dashboard UIs to surface source labels and hide models excluded by
all active connections.

config/payloadRules.json

@@ -0,0 +1,6 @@
+{
+  "default": [],
+  "default-raw": [],
+  "override": [],
+  "filter": []
+}