feat: Thread optional `phase` param into `db/sessions.ts::cre… (+7 more)

- ✅ Thread optional `phase` param into `db/sessions.ts::createSession()`
- ✅ Thread optional `phase` param into `ipc/handlers.ts` sessions:create handler
- ✅ Thread optional `phase` param into `preload.ts` createSession API
- ✅ Update Plan phase system prompt to gracefully handle missing research.md
- ✅ Update Implement phase system prompt to gracefully handle missing plan.md
- ✅ Create `renderer/src/components/NewSessionModal.tsx`
- ✅ Update `App.tsx`: add modal state, split handler, add modal JSX
- ✅ Add modal CSS to `globals.css`

1 files changed, 3 insertions, 2 deletions

diff --git a/src/main/claude/index.ts b/src/main/claude/index.ts
index 8cf512c..9139f17 100644
--- a/src/main/claude/index.ts
+++ b/src/main/claude/index.ts
@@ -48,8 +48,9 @@ export async function sendMessage({
   // Load any custom system prompt for this phase (null → use default)
   const customSystemPrompt = getSetting(`systemPrompt.${session.phase}`) ?? undefined;
 
-  // Load global model override (empty string or null → let SDK use its default)
-  const configuredModel = getSetting("model") || undefined;
+  // Phase-specific model override takes precedence; falls back to global default.
+  const configuredModel =
+    getSetting(`model.${session.phase}`) || getSetting("model") || undefined;
 
   // Load MCP servers config (JSON string → object, or undefined if not set)
   const mcpServersJson = getSetting("mcpServers");