feat: layer runtime and model selection across conversation, project and global

- Store runtime selection as { provider?, model? } layers and resolve them per
  field (conversation -> project -> global); drop the legacy auto provider.
- Migrate stored selections (database v49) and clear deleted profile ids.
- Re-resolve selections in Main per request and at queue dispatch.
- Add ProjectRuntimeSelector and a two-column RuntimeModelPicker; manage
  link opens model connections; restore per-runtime default model tabs.
- Stop duplicating trusted instructions and history across OpenCode,
  Continue and DeepSeek Harness runtimes.
- Document the layered design, global provider removal plan and planned
  purpose-specific models.

src/renderer/src/SettingsPanel.tsx

@@ -1645,7 +1645,9 @@ export function SettingsPanel({
               provider: agentRuntimeType,
               profileId: runtimeSource.profileId
             }
-          : { provider: agentRuntimeType }
+          : runtimeSource.kind === 'platform'
+            ? { provider: agentRuntimeType, runtimeConfig: true as const }
+            : { provider: agentRuntimeType }
       const status = testingModel
         ? await window.goodbuddy.settings.testModelConnection(profileId)
         : await window.goodbuddy.settings.testRuntime(runtimeSelection)
@@ -3563,10 +3565,10 @@ export function SettingsPanel({
                         'openai-images-generations'
                           ? t('model.profile.imageGeneration')
                           : t('model.profile.textChat'),
-                      continueCompatibility: isContinueCompatible(profile)
+                      continueCompatibility: isAgentRuntimeModelProtocol(profile.protocol)
                         ? t('model.profile.compatible')
                         : t('model.profile.incompatible'),
-                      openCodeCompatibility: isOpenCodeCompatible(profile)
+                      openCodeCompatibility: isAgentRuntimeModelProtocol(profile.protocol)
                         ? t('model.profile.compatible')
                         : t('model.profile.incompatibleImageProtocol'),
                       deepseekHarnessCompatibility: