feat(obsidian): pre-warm vault cache on startup for instant browsing

Problem: The first time you browse notes, it has to scan all 13,496 files,
which is very slow. This makes the initial user experience poor.

Solution: Pre-warm the vault file cache in the background:
1. When Obsidian connection is tested (first-time setup)
2. When FMG loads and Obsidian is already enabled (page reload)

Implementation:
- Add prewarmCache() function that scans vault in background
- Call it from testConnection() (don't await - runs async)
- Call it from init() if config.enabled is true
- Scan happens silently in the background
- By the time user clicks Browse, cache is already loaded

Benefits:
- First browse is instant (cache already loaded)
- Works on every page reload
- Non-blocking (doesn't slow down FMG startup)
- Silent/automatic (no user interaction needed)

User experience:
- First time: Test connection → cache warms in background → browse is instant
- Subsequent loads: Page loads → cache warms → browse is instant
- Cache lasts 5 minutes, so multiple browses within that window are all instant
EOF
)

modules/io/obsidian-bridge.js

@@ -46,6 +46,12 @@ const ObsidianBridge = (() => {
         fmgIdIndex = {};
       }
     }
+
+    // Pre-warm cache if Obsidian is already enabled
+    if (config.enabled) {
+      INFO && console.log("Obsidian enabled, pre-warming cache...");
+      prewarmCache();
+    }
   }
 
   // Save configuration
@@ -74,6 +80,10 @@ const ObsidianBridge = (() => {
       INFO && console.log("Obsidian connection successful:", data);
       config.enabled = true;
       saveConfig();
+
+      // Pre-warm the cache in the background (don't await)
+      prewarmCache();
+
       return true;
     } catch (error) {
       ERROR && console.error("Obsidian connection failed:", error);
@@ -83,6 +93,18 @@ const ObsidianBridge = (() => {
     }
   }
 
+  // Pre-warm the vault files cache in the background
+  async function prewarmCache() {
+    try {
+      INFO && console.log("Pre-warming vault file cache...");
+      await getVaultFiles();
+      INFO && console.log("Vault file cache pre-warmed successfully!");
+    } catch (error) {
+      WARN && console.warn("Failed to pre-warm cache:", error);
+      // Don't throw - this is just optimization
+    }
+  }
+
   // Recursively scan a directory and all subdirectories for .md files
   async function scanDirectory(path = "") {
     const response = await fetch(`${config.apiUrl}/vault/${encodeURIComponent(path)}`, {