feat: URL-derived provider keys (hs-<hostname>) + dedup providers sharing same gateway URL

- GatewayProviderKey() derives stable key from gateway URL hostname
  e.g. https://llmgw.h.raczylo.com/v1 → hs-llmgw-h-raczylo-com
- AbsorbDuplicateProviders() merges providers sharing the same baseURL
  into our canonical entry; user-crafted model metadata wins for overlaps
- kilo: renders to opencode.jsonc (primary config), deep-merges providers,
  deletes enabled_providers filter that was hiding our gateway
- opencode: absorbs duplicate providers from existing config
- All adapters use GatewayProviderKey() instead of hardcoded string
- Fix goose URL doubling (was /v1/v1/chat/completions → /chat/completions)
- Fix token propagation: api_key written directly (not env var ref)
- Zed: adds prompt_cache_key capability, deletes context_servers key
  to avoid ContextServerSettingsContent serde untagged-enum parse error

internal/adapter/common/dedup.go

@@ -0,0 +1,69 @@
+package common
+
+import "maps"
+
+// AbsorbDuplicateProviders scans provMap for entries (other than ourKey) whose
+// options.baseURL matches gatewayURL and absorbs their models into our entry.
+//
+// Merge strategy:
+//   - Models only in the duplicate: added to our provider.
+//   - Models only in our canonical entry: kept as-is.
+//   - Models in both: the DUPLICATE's entry wins (preserves user-crafted display
+//     names and custom limits that are often more descriptive than the profile
+//     alias).
+//
+// Absorbed entries are deleted from the returned map. Returns provMap unchanged
+// when gatewayURL is empty or our entry is absent.
+func AbsorbDuplicateProviders(provMap map[string]any, ourKey, gatewayURL string) map[string]any {
+	if gatewayURL == "" || provMap == nil {
+		return provMap
+	}
+	ourEntry, ok := provMap[ourKey].(map[string]any)
+	if !ok {
+		return provMap
+	}
+
+	// Clone top-level so we don't mutate the caller's map.
+	result := make(map[string]any, len(provMap))
+	maps.Copy(result, provMap)
+
+	ourModels, _ := ourEntry["models"].(map[string]any)
+	if ourModels == nil {
+		ourModels = map[string]any{}
+	}
+
+	// merged starts with our canonical models; duplicates may override per-model.
+	merged := make(map[string]any, len(ourModels))
+	maps.Copy(merged, ourModels)
+
+	for k, v := range result {
+		if k == ourKey {
+			continue
+		}
+		entry, ok := v.(map[string]any)
+		if !ok {
+			continue
+		}
+		opts, _ := entry["options"].(map[string]any)
+		if opts == nil {
+			continue
+		}
+		if opts["baseURL"] != gatewayURL {
+			continue
+		}
+		// Same gateway URL — absorb and delete.
+		if dupModels, ok := entry["models"].(map[string]any); ok {
+			// Duplicate (user-crafted) wins for overlapping IDs.
+			maps.Copy(merged, dupModels)
+		}
+		delete(result, k)
+	}
+
+	updated := make(map[string]any, len(ourEntry))
+	maps.Copy(updated, ourEntry)
+	if len(merged) > 0 {
+		updated["models"] = merged
+	}
+	result[ourKey] = updated
+	return result
+}