Show syntax errors in the scripting terminal editor

[rubensworks]

Replaces #80, with the same changes as one standalone commit. Phase 4 of the scripting terminal UX improvements, stacked on #86 (then #85).

Problem

A syntax error in a script only became visible once a variable card using it was evaluated, e.g. as an X in a display panel that you then had to hover (see #5). The terminal itself gave no feedback, and the info book said so too.

Changes

• ILanguageHandler gets a default checkSyntax(Path, String) that returns null, so other language handlers keep working.
• The JavaScript handler implements it with GraalJS Context.parse, which parses the script without executing it.
• The server checks the active script once it has been unchanged for 10 ticks, and only re-checks when the content changes. The result goes to the client in a new TerminalScriptingSyntaxErrorPacket.
• The editor underlines the error position, turns the line number red and gives that gutter cell a light red background, and shows a red tick on the scrollbar at the error's position, so an error that is scrolled out of view is still visible. Hovering the line shows the message.
• The info book text that said the editor can't detect syntax errors is updated (en_us only).

Validation

In a dev client (clientdevbridge), with a missing ) on line 7 of a 40-line script:

• Before: nothing in the editor indicates a problem.
• After: line 7's gutter is red, the ; is underlined, and hovering shows SyntaxError: script0.js:7:23 Expected , but found ;. Typing the missing ) clears all markers.
• Scrolled down to line 11: before, there was no sign of the error; now the red tick on the scrollbar stays visible.

New unit tests check the result for valid code, a syntax error (line and column), an unclosed block, and that throw new Error(...) isn't executed.

Dropped from the original plan

• An "unsynced changes" indicator: edits sync every second and on close, so it would show for under a second and doesn't fix a real problem.

Testing

• ./gradlew build passes, including the new unit tests.
• ./gradlew runGameTestServer: all 23 tests pass.
• I didn't add a game test for the server-side debounce, because it needs an open container with a real player connection to observe the packet. The checker itself is covered by the unit tests.

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[github-actions]

Coverage Report for CI Build 39152695741

Coverage at 44.072% (no base build to compare)

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	3402
Covered Lines:	1641
Line Coverage:	48.24%
Relevant Branches:	1397
Covered Branches:	474
Branch Coverage:	33.93%
Branches in Coverage %:	Yes
Coverage Strength:	23.43 hits per line

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