feat(dashboard): Rhai source formatter with Format button

AST-based pretty-printer: tab-indented, 100-col print width, normalized
operator spacing, predictable reflow of long argument lists, comments
preserved verbatim. Refuses to emit on a parse failure and returns the
first error, so the Edit-tab button mirrors the JSON Format UX —
inline `.error.inline` banner; doc untouched on failure.

Patch bump to `0.5.1` across Cargo.toml workspace.package, the
dashboard package.json, and the docs/versioning.md Current versions
table.

Bundle delta versus the previous build: +6 KB raw, +1.5 KB gzipped.
Cumulative since the start of this work: +28 KB raw, +7.3 KB gzipped —
well under the +100 KB budget.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dashboard/package.json

@@ -1,6 +1,6 @@
 {
   "name": "picloud-dashboard",
-  "version": "0.5.0",
+  "version": "0.5.1",
   "private": true,
   "type": "module",
   "scripts": {