DBX SSH plugin 0.7.6-beta.3

预发布基线说明（延续 beta.1）：调度任务（task-provider）功能声明在本预发布线继续摘除——DBX 上游尚未发布宿主侧 task-provider 能力。sidecar task/* 实现与本地 Shell 连接类型保留，待上游发布后恢复。
Pre-release note (carried over from beta.1): the scheduler task-provider contribution stays withheld on this line — the DBX host has not shipped the task-provider capability yet. The sidecar task/* implementation and the Local shell connection type are kept; the declaration returns once upstream ships.

• 本地 Shell：启动目录、环境变量与「选择 Shell 打开」。local/terminal/start 新增 env 参数（逐条净化）；io.dbx.ssh.local 连接表单新增 cwd/env 字段；设置菜单新增「启动目录 + 环境变量编辑器」；会话菜单新增「选择 Shell 打开」子页（一次性 override）；本地模式面板收口三层防线，修掉 SSH 分栏切本地的幽灵分栏。
  Local shell: working directory, environment variables, and "Open with Shell". local/terminal/start gains a sanitized env parameter; the local connection form gains cwd/env fields; settings gains a startup-directory + environment editor; the session menu gains an "Open with Shell" subpage (one-shot override); and local-mode panel collapse gets three layers of defense against ghost split panes.

• Docker：容器 shell 退出后不再接力（#182）。bash || zsh || … 链在非零退出后继续启动后续 shell——exit 后仍留在容器内；现改为 command -v 探测后 exec 启动，任意退出即结束会话并保留退出码。
  Docker: container shell no longer chains after exit (#182). The old bash || zsh || … fallback kept starting the next shell after a non-zero exit; it now probes with command -v and execs, so any exit ends the session and preserves the exit code.

• Docker：表格横向滚动三修（0.7.5 修复回流）。0.7.5 发布的滚动条可见 + 名称/操作列粘性修复未回流主线、0.7.6 系列一度退化；本次自 0.7.5 发布线收编。
  Docker: table horizontal scrolling (0.7.5 fix carried over). The scrollbar-visibility and sticky column fixes shipped in 0.7.5 but never returned to the mainline and regressed in 0.7.6; brought back from the 0.7.5 release line.

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安装包由发布流水线在 5 个平台自动构建（darwin-arm64 / darwin-x64 / linux-x64 / linux-arm64 / windows-x64），构建完成后自动附加到本 Release。