feat(lanes,run,pricing): Changes sidebar editor, staged groups, image drop, auto pricing

- Changes panel at full screen: the whole Files view (finder, expand-all,
  tree) becomes a left sidebar and the Files tab is dropped; a working-copy
  file opens straight into the editor (Save/Cancel live once the text
  differs, Cancel restores it, Whole file toggles back to the diff), and the
  page is height-locked so the editor no longer collapses with no live run.
- Overview splits into Staged Changes / Changes groups in the work range.
- A changed file's whole tree row takes its status tint.
- Drag an image onto the lane terminal: POST /api/run/drop-image saves it
  (png/jpeg/gif/webp, random name, 0600, pruned after a day) and the path
  is pasted into the pane, which is how claude attaches it.
- Claude Opus 5.5 gets its own pricing row (4/20/0.2/5/8, fast 8/40);
  claude-opus-5% had been pricing it as Opus 5.
- server/lib/pricing-sync.js: a model family used in token_usage with no
  row of its own is inserted from LiteLLM's public price list, never
  updated; off with AGENTHUB_PRICING_SYNC=0. repo-links allows exactly
  that one third-party GitHub raw URL.

server/index.js

@@ -325,6 +325,9 @@ function startBackgroundServices() {
   // One-time legacy-session backfill (a no-op once its marker file exists).
   autoImportLegacySessions();
 
+  // Rates for models seen in token_usage with no pricing row of their own.
+  require("./lib/pricing-sync").startPricingSync(require("./db").db);
+
   // A provisioning job belongs to the previous Node process and cannot survive
   // a restart. Recover those rows now so the dashboard never shows a permanent
   // provisioning spinner for work that was interrupted by the restart.