Linux, Windows import and harness fixes

Fixed

Ctrl+Z and Ctrl+Shift+Z undo and redo in the composer and other text fields, which WebKitGTK didn't do on its own (#277).
Pasting a copied image works on Wayland, including screenshots from Flameshot, when the paste carries no file (#272). Large images are scaled down before they're attached.

ACP harnesses without the selected mode keep running. A harness that has no Plan or Accept edits mode now runs in its own current mode and says which one it used. It refuses instead if that mode looks more permissive than the one you picked (#269).
Claude Code no longer shows as Unavailable when its startup reply is over 256 KiB (#276).
DeepSeek harness skills appear in the slash menu (#278).
The capability inventory finds OpenCode MCP servers set up in opencode.jsonc, including files with comments and trailing commas (#275).

Importing conversations works on Windows. Codex conversations were filtered out because of how Windows writes folder paths, so the import listed nothing (#273).
A project whose folder you renamed or moved can be relinked. "Project folder is unavailable" now offers Locate folder. Its worktrees are repaired to point at the new location (#268).

Cloud sandboxes settings: the environment checkbox is normal size with its help mark beside it, and connected providers are listed first (#283).

Thanks to @hongkongkiwi and @AbuSeRik for the pull requests these fixes started from.

The Wayland paste and Linux undo fixes were tested in browsers, not on a real Linux desktop.
The Windows import fix was tested with Windows-style paths on macOS, not on Windows. Importing Claude Code conversations on Windows looked correct in the code, but we couldn't reproduce the report.
PandaCode decides whether a harness mode is more permissive by its name, so a permissive mode with an unusual name could still be used.

macOS (Apple silicon): open PandaCode-macOS-arm64.dmg and drag PandaCode to Applications. This build is signed and notarized, so macOS opens it without a warning.
macOS (Intel): the same, with PandaCode-macOS-x64.dmg.
Windows x64: run PandaCode-Windows-x64-setup.exe. If SmartScreen warns about an unknown publisher, choose More info > Run anyway.
Windows arm64: run PandaCode-Windows-arm64-setup.exe (same SmartScreen step).
Linux x64: chmod +x PandaCode-Linux-x86_64.AppImage and run it.
Linux arm64: chmod +x PandaCode-Linux-aarch64.AppImage and run it.
Any of the above, from a terminal: npx pandacode downloads, verifies and installs the right build, and signs it locally on macOS, so no Gatekeeper warning appears.

Each file has a .sha256 checksum beside it. Installed copies update themselves from this page. Build from source: see CONTRIBUTING.md.