Mark code in every message with backticks: blue in the CLI, code font in the IDE #532

Messages mix our own words with code and spec expressions, and nothing tells them apart:

State Refinement Error: found markState(buffered) == unmarked but expected markState(buffered) == marked
Call buffered.mark(int) before this call; afterwards markState(buffered) == marked
Origin: line 134, new BufferedInputStream(stream) makes markState(buffered) == unmarked

Proposal (PM, 2026-11-10)

Every message that shows code marks it, not just the notes. That covers:

• headlines (found … but expected …, expected … but could not prove it);
• hints;
• message notes (Origin:);
• the declared-here gloss (where … means …);
• counterexamples.

The marker is backticks inside the message string: found `markState(buffered) == unmarked` but expected `markState(buffered) == marked` .

• CLI: show each code span in blue (ANSI) without the backticks. With colour off (NO_COLOR, or not a terminal), keep the backticks, as rustc does.
• Plain-text consumers (the Problems tab, the diagnostic hover): get the string with backticks, which reads like rustc's messages.
• IDE panel: renders each span in the editor font (vscode-liquidjava#192).
• Escaping: code that itself contains a backtick needs escaping or a longer fence; char/string literals rarely do.

Line references (line 134) also carry their file and position in the diagnostic data, so the IDE can make them clickable.