feat(windows): ship an installer, with the zip as the portable option

[StuartCameronCode]

Stacked on #113 (base linux-appimage) — both touch the same release scripts, README table and packaging_test.dart. Merge #113 first; GitHub will retarget this to main.

Summary

The Windows release was a zip to extract and run. It now also ships an Inno Setup installer built from the same tree: Start menu shortcut, optional desktop shortcut, an entry in Settings → Apps. The zip stays as the portable option.

• packaging/windows/vapourbox.iss (new) — the installer definition.
• Scripts/build-windows-installer.ps1 (new) — compiles it from an assembled package directory; checks the tree is complete first.
• package-windows.ps1 — calls it after zipping. -SkipInstaller gives the zip alone.
• build-windows.yml — installs Inno Setup, builds the installer, uploads -setup.exe + .zip.
• ci-build-and-release.sh, release.sh — the release upload picks up *-setup.exe; release-notes text updated.
• packaging_test.dart — three lint tests (below).
• Docs — README install steps and download table, docs/BUILDING.md, a Windows section in CLAUDE.md.

Design notes

• Per-user only (PrivilegesRequired=lowest), no all-users option. On Windows the app downloads deps and add-ons into deps\ and addons\ next to the executable, so the install directory must stay user-writable. It installs to %LOCALAPPDATA%\Programs\VapourBox and never prompts for admin. A lint test ties this restriction to the line in dependency_manager.dart that makes it necessary.
• Upgrade keeps deps\/addons\; uninstall removes them. [InstallDelete] clears templates\ and data\ before an upgrade, because Inno never removes a file a newer version dropped and exe_dir\templates is the first path the worker searches. Saved presets are left alone.
• Its own script, not part of package-windows.ps1, because build-windows.yml assembles the package inline rather than calling that script (and the two zips differ in layout). That pre-existing split is untouched here.
• Inno Setup pinned to 6.7.3 by SHA-256, not 7.x: the .iss is written against 6.

Not changed

• The installer is unsigned, like the rest of the Windows build, so SmartScreen warns on it. The README tells users to choose More info → Run anyway. Removing the warning needs a code-signing certificate.
• The zip's contents and layout.

Test plan

• flutter test test/packaging_test.dart passes locally (10 tests)
• The installer has not been compiled yet — it needs Inno Setup on Windows. build-windows.yml dispatched on this branch; result to follow in a comment.
• Run the installer on Windows 10/11: no UAC prompt, Start menu shortcut, first-launch deps download succeeds, a job encodes
• Install an older build then this one: deps are kept, no second entry in Settings → Apps
• Uninstall: deps\ and addons\ are gone, %USERPROFILE%\.vapourbox is not

🤖 Generated with Claude Code

https://claude.ai/code/session_014GLXdGLfPwgYjW1AkonGqN

[StuartCameronCode]

Test builds of this branch are green: https://github.com/StuartCameronCode/VapourBox/actions/runs/37303191178 (version 0.0.1, deps-v1.12.0).

• The .iss compiles; the artifact holds VapourBox-0.0.1-windows-x64-setup.exe (~13 MB) and the .zip (~16 MB).
• The first build compiled with the runner image's own ISCC.exe (a Chocolatey shim on PATH) rather than the pinned 6.7.3. Fixed in f3db8bf: the pinned copy installs to its own directory and is passed as $ISCC. The second build's log confirms D:\a\_temp\InnoSetup-6.7.3\ISCC.exe did the compiling.
• CI Tests pass on all four platforms at f3db8bf, including the CRLF fix for the lint tests on a Windows checkout.

Still unchecked: running the installer on a real Windows machine (no UAC prompt, first-launch deps download, upgrade, uninstall).

🤖 Generated with Claude Code