fix: populate script isRtl in controller and svelte

[andrew-polk]

What

Adds feature parity for the newly-added IScript.isRtl property across the controller and Svelte language choosers. isRtl was previously populated only by the React hook.

Changes

• Controller (language-chooser-controller): a scriptWithReadingDirection() helper stamps isRtl (via isRTLScript(script.code)) onto the selected script at every path a script becomes selected — normal selection, auto-selection of a language's sole script, and customize-modal submit. It returns a fresh copy rather than mutating shared language data, which matches the Field change-detection contract. Svelte consumers (which derive the emitted orthography from selectedScript) now receive the reading direction automatically.
• Svelte demo (BasicDemo.svelte): the "Submitted selection" panel shows the script as Name (RTL/LTR), matching the React DialogDemo.
• find-language (isRTLScript): wrapped Intl.Locale construction in try/catch so a malformed/unknown script code returns false instead of throwing. Behavior for valid codes is unchanged.
• Tests: updated controller specs whose exact-equality assertions now include the populated isRtl, and added a test asserting isRtl: true for an RTL script (Arabic).

Verification

• controller: typecheck ✓, lint ✓, 95 tests ✓
• find-language: typecheck ✓, lint ✓, 172 tests ✓
• react-hook: 16 tests ✓ (shared isRTLScript change)
• svelte: typecheck ✓, svelte-check ✓, tests ✓

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This change is 

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Devin review

[andrew-polk]

[Claude Opus 4.8] Consulted Devin on 2026-07-24 10:59 USMST up to commit 524b0418c5a1f1e70b3142f1f9e7eeb87ba4ce1e.

Result: 0 Bugs, 0 Investigate flags, 1 Informational (not mirrored — low signal). The informational note observes that isRtl is now always populated as a concrete boolean (never left undefined) on the controller's selection paths; Devin itself concludes this is consistent with the existing React hook and not a bug. It is the intended parity behavior, so nothing to act on. Nothing to mirror to the PR.

[andrew-polk]

[Claude Opus 4.8] Consulted Devin on 2026-07-24 11:14 USMST up to commit 6b5cf77e677a7032df3588efe6a1563a93393a06 (after squashing to a single fix: commit; content unchanged).

Result: 0 Bugs, 0 Investigate flags, 3 Informational (not mirrored — low signal, no action). Re-review clean.