fix(dashboard): preserve blank lines and improve Rhai parser errors

Two follow-ups on the Rhai formatter shipped in 0.5.1.

* Formatter no longer collapses user-intent blank lines between
  statements. The lexer now records a side-channel list of offsets
  where the source contained two-or-more consecutive newlines; the
  formatter consults it and emits a single blank in the same spot
  (rustfmt's `blank_lines_upper_bound = 1` policy applied strictly —
  the prior forced blank between top-level `fn` decls is dropped, so
  the formatter never *adds* a blank the user didn't write).
* Parse errors now read like Rhai's own diagnostics. `expect()` takes
  an optional `role` hint and each call site supplies a domain phrase
  (`name of a variable`, `function name in function declaration`,
  `'{' to begin a block`, `name of a property`, …). End-of-input is
  reported as `script is incomplete`. The dashboard banner renders
  `Parse error: {message} (line L, position C)` with 1-based
  coordinates, matching Rhai's format exactly.

The FormatError payload also keeps the byte `offset` so callers that
want to drive the editor cursor (CodeMirror works in offsets) still
have it.

Also folds the workspace Cargo.lock version bumps for 0.5.1 — the
lock-file rewrite that should have travelled with the prior commit.

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

dashboard/src/lib/rhai/ast.ts

@@ -272,4 +272,8 @@ export interface ParseResult {
 	program: BlockExpr;
 	errors: ParseError[];
 	comments: Comment[];
+	// Offsets at which the source contained a blank line (a whitespace
+	// run with two or more newlines). One entry per blank run; the
+	// formatter consults these to preserve user-intent vertical grouping.
+	blankLines: number[];
 }