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/adapters/crush/crush_test.go

@@ -44,8 +44,8 @@ func TestCrushRenderProducesExpectedTargets(t *testing.T) {
 	// providers must be a map (not array), keyed by providerID.
 	providers, ok := parsed["providers"].(map[string]any)
 	require.True(t, ok, "providers must be a map")
-	gw, ok := providers["harness-sync-gateway"].(map[string]any)
-	require.True(t, ok, "harness-sync-gateway provider missing")
+	gw, ok := providers["hs-gw"].(map[string]any)
+	require.True(t, ok, "hs-gw provider missing")
 	assert.Equal(t, "openai-compat", gw["type"])
 	// models must be role-map with large/small/title.
 	models, ok := parsed["models"].(map[string]any)
@@ -137,7 +137,7 @@ func TestCrushRenderProducesMapProvidersAndRoleModels(t *testing.T) {
 	// providers is a map, not an array.
 	providers, ok := parsed["providers"].(map[string]any)
 	require.True(t, ok, "providers must be a map")
-	gw, ok := providers["harness-sync-gateway"].(map[string]any)
+	gw, ok := providers["hs-gw"].(map[string]any)
 	require.True(t, ok)
 	assert.Equal(t, "openai-compat", gw["type"])
 	assert.Equal(t, "https://gw", gw["base_url"])
@@ -160,7 +160,7 @@ func TestCrushRenderProducesMapProvidersAndRoleModels(t *testing.T) {
 		sel, ok := roleModels[role].(map[string]any)
 		require.True(t, ok, "role %s missing", role)
 		assert.Equal(t, "claude-sonnet-4-6", sel["model"])
-		assert.Equal(t, "harness-sync-gateway", sel["provider"])
+		assert.Equal(t, "hs-gw", sel["provider"])
 	}
 }