feat: v0.3.0 - fix provider data loss, oauth corruption & switch UX

Bug fixes:
- Fix config.toml wiped to single provider on switch (now writes all providers)
- Fix managed:kimi-code oauth key corruption (oauth/kimi-code was rewritten
  to oauth/managed-kimi-code, breaking the official subscription)
- Fix default_model not switching due to React 18 deferred state update
  (updateConfig now sets configRef synchronously before setConfig)
- Strip KimiSwitch-private default_model from config.toml provider output

Architecture:
- config.toml is now the authoritative source for Kimi Code provider data
- SQLite stores only metadata (notes, official URLs, remembered models)
- Load reconciles config.toml with SQLite for external /provider changes
- Activate is a no-op for KimiCode (save already writes config.toml)

Features:
- Selected provider moves to top of list on switch
- Add models-dev context size lookup
- Add tauri-plugin-single-instance

Tests:
- 3 new regression tests: oauth key round-trip, all-providers write,
  private default_model strip

src/App.tsx

@@ -6,6 +6,7 @@ import { ProviderList } from "./components/ProviderList";
 import { ProviderEdit } from "./components/ProviderEdit";
 import { useTranslation } from "./i18n";
 import { getDefaultMaxContextSize } from "./lib/model-defaults";
+import { getModelRef } from "./lib/models-dev";
 import type { Agent, Model, Provider } from "./types";
 
 const AGENT_STORAGE_KEY = "kimi-switch-agent";
@@ -242,26 +243,31 @@ export default function App() {
         }
       }
 
-      // Only the selected provider is active. All other providers (including
-      // Kimi native/managed and custom) are deactivated so the target agent
-      // follows Kimi Switch's choice exactly.
+      // Rebuild providers with the selected one moved to the front so it is
+      // visually prioritised. All others are deactivated.
       const providers: Record<string, Provider> = {};
-      for (const [key, p] of Object.entries(cfg.providers)) {
-        providers[key] = { ...p, active: key === name };
-      }
+      providers[name] = { ...target, active: true };
 
-      // Remember the active provider's current default model (if it belongs to
-      // that provider) so switching back later restores the user's choice.
-      if (activeProviderName && cfg.default_model) {
-        const activeProvider = providers[activeProviderName];
-        if (activeProvider && cfg.models[cfg.default_model]?.provider === activeProviderName) {
+      // Remember the old active provider's current default model (if it
+      // belongs to that provider) so switching back later restores the user's
+      // choice.
+      if (activeProviderName && activeProviderName !== name && cfg.default_model) {
+        const oldActive = cfg.providers[activeProviderName];
+        if (oldActive && cfg.models[cfg.default_model]?.provider === activeProviderName) {
           providers[activeProviderName] = setProviderDefaultModel(
-            activeProvider,
+            { ...oldActive, active: false },
             cfg.default_model
           );
         }
       }
 
+      // Add remaining providers (skip selected and old-active if already added).
+      for (const [key, p] of Object.entries(cfg.providers)) {
+        if (key === name) continue;
+        if (providers[key]) continue;
+        providers[key] = { ...p, active: false };
+      }
+
       // Prefer the target provider's remembered default model; fall back to
       // its first model when there is no saved preference or it is invalid.
       let default_model = getProviderDefaultModel(target);
@@ -315,7 +321,10 @@ export default function App() {
           ...m,
           alias,
           provider: provider.name,
-          max_context_size: m.max_context_size ?? getDefaultMaxContextSize(m.model),
+          max_context_size:
+            m.max_context_size ??
+            getModelRef(m.model)?.context ??
+            getDefaultMaxContextSize(m.model),
         };
       }