chore(release): 准备 v0.20.3

[feigeCode]

Description

Release preparation for v0.20.3: the version bump (main/Cargo.toml, Cargo.lock) plus the bilingual CHANGELOG.md entry. This is a release-only PR — no product code changes — so CI takes the dedicated fast path (script/release_pr.py check reports release_only=true and validates the release metadata instead of running the full platform matrix).

Everything this release ships is already on main since v0.20.2:

• Terminal scrolling (feat: add terminal scrolling by lines and pages #409): Ctrl+Shift+Up/Down scrolls one line, Shift+PageUp/PageDown scrolls a screen; both rebindable in Settings.
• Sticky Auto-mode SQL sessions (issue [Feature]: 希望支持数据库变量 #312): repeated runs in one editor tab reuse the same database connection, so SET @var and other session state survive across executions.
• Notes / Markdown editor (feat: 同步 velotype #116/#119/#121/#125 优化 #406): collapsible outline panel on the right (Cmd/Ctrl+Shift+O), Markdown code font setting, plus upstream velotype fixes (double-click word selection, IME crash, div block image/link layout).
• SFTP (issues [Feature]: sftp这里 能不能搞个 点击之后下拉硬盘列表 #276/[Bug]: sftp 地址栏输入 D: 打开的路径不对，输入 D:\ 就可以 #375, fixed: 处理目录上传扫描中的符号链接，以防止上传失败 #417, fix(sftp): 上传卡死可立即取消、快速失败，同连接传输并发车道 #418): Windows disk dropdown restored and bare drive letters accepted in the address bar; uploads can be cancelled immediately and fail fast (request timeout 300s → 60s); three concurrent transfer lanes per SSH connection; directory uploads with symlinks no longer fail as a whole.
• Redis (issue [Bug]: Redis「集群」模式只列出其中一个节点的 key，不会汇总所有 master #414, [Bug]: 键树渲染 zset 类型徽章时整个应用崩溃（gpui text.rs:650 unwrap on None） #416): "Enable TLS" works again (the TLS feature was never compiled in), cluster mode aggregates every master with MOVED redirection, and the empty-database / zset badge crashes are fixed.
• Database (fix(db): 清空表后自动刷新表数据页签（TRUNCATE 与全表 DELETE 的数据级失效通知） #413): truncating a table refreshes the table data tab; saving from the result grid no longer duplicates the schema prefix (42S02 / 1146).
• Clipboard (fix(clipboard): 复制 JSON 字段不再多包一层引号，剪贴板内容等于存储原文 #412): copying a JSON field no longer wraps it in extra quotes.

Screenshot

Not applicable — this PR only carries release metadata (CHANGELOG.md + version bump).

How to Test

• python3 script/changelog.py validate --tag v0.20.3 --changelog CHANGELOG.md → Validated changelog entry: v0.20.3.
• python3 script/changelog.py extract --tag v0.20.3 --changelog CHANGELOG.md round-trips the same Markdown that will become the GitHub Release body and the R2 release_notes.
• BASE_SHA=<origin/main> HEAD_SHA=<head> python3 script/release_pr.py check → release-only: True and release metadata validated for v0.20.3.
• After merge: script/release-tag.sh v0.20.3 on main verifies the version and tag consistency before pushing the tag that triggers the Release workflow.

Checklist

• I have read the CONTRIBUTING document and followed the guidelines.
• Reviewed the changes in this PR and confirmed AI generated code (If any) is accurate.
• Passed cargo run for story tests related to the changes. — Not applicable: release metadata only, no code change.
• Tested macOS, Windows and Linux platforms performance (if the change is platform-specific) — Not applicable for the same reason; each fix was validated by the CI matrix on its own PR.