feat: add Greenplum 7 compatibility and AI SQL generation

Greenplum 7 (PG12-based) compatibility:
- Auto-detect GP via version() string, store DbFlavor per connection
- connect returns ConnectResult with version + flavor
- Fix pg_total_relation_size to use c.oid (universal, safer on both PG/GP)
- Branch is_identity column query for GP (lacks the column)
- Branch list_sessions wait_event fields for GP
- Exclude gp_toolkit schema in schema listing, completion, lookup, AI context
- Smart StatusBar version display: GP shows "GP 7.0.0 (PG 12.4)"
- Fix connection list spinner showing on all cards during connect

AI SQL generation (Ollama):
- Add AI settings, model selection, and generate_sql command
- Frontend AI panel with prompt input and SQL output

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/models/ai.rs

@@ -0,0 +1,44 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AiSettings {
+    pub ollama_url: String,
+    pub model: String,
+}
+
+impl Default for AiSettings {
+    fn default() -> Self {
+        Self {
+            ollama_url: "http://localhost:11434".to_string(),
+            model: String::new(),
+        }
+    }
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct OllamaChatMessage {
+    pub role: String,
+    pub content: String,
+}
+
+#[derive(Debug, Serialize)]
+pub struct OllamaChatRequest {
+    pub model: String,
+    pub messages: Vec<OllamaChatMessage>,
+    pub stream: bool,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct OllamaChatResponse {
+    pub message: OllamaChatMessage,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct OllamaTagsResponse {
+    pub models: Vec<OllamaModel>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OllamaModel {
+    pub name: String,
+}