TP-30 — Release docs and QA checklist for custom themes

[ZhuchkaTriplesix]

Epic: E
Depends on: TP-01 through TP-29

Source: docs/theme-parser-github-issues.md

Goal

Prepare the feature for release and manual verification.

Files

• docs/theme-custom-json.md
• docs/theme-import.md
• docs/release-checklist.md
• CHANGELOG.md when release branch is prepared.

Implementation

Add QA checklist:

• import valid custom dark;
• import valid custom light;
• import VS Code JSONC;
• select among 50+ fake themes or test pack;
• restart app and verify selected theme persists;
• delete selected theme file and restart;
• verify fallback + Preferences error;
• verify title bar/window controls colors;
• verify SQL/JSON highlighting still uses tokenColors.

Acceptance Criteria

• Release checklist includes custom theme scenarios.
• Docs include troubleshooting for invalid colors/missing fields.
• CHANGELOG entry can be written from completed issues.

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Optional follow-up issues

These are intentionally out of the first implementation pass.