Add preview styles for cell source and outputs

Introduce CSS for compact previews of notebook cells: .verso-cell-source-preview (margins, padding, border, rounded background and font styles) and .verso-cell-output-summary (dashed summary box). Add rules to clamp text/output previews (.verso-cell-outputs--preview and .verso-cell-rendered-input--preview) using -webkit-line-clamp and to limit HTML output height. Uses existing CSS variables for colors, spacing and font sizes to match theming and keep previews concise.

Support extension directory and more polyglot .ipynb language switches

Allow loading third-party Verso extensions from a user-specified directory and add support for Polyglot Notebook language-switching when importing Jupyter notebooks. Adds an ExtensionsDirectory field to notebook open params and loads assemblies from that path in the host; exposes a vscode setting (verso.extensionsPath) and forwards it from the editor. Introduces JupyterPolyglotPostProcessor to split and remap #!language directives into proper cells, updates DibSerializer with additional language aliases (cs, fs, py, ts, python, typescript, etc.), and adds/updates unit tests to cover the new processor and aliases. Also updates expected built-in extension count accordingly.

Rename publish command to export

Rename PublishCommand to ExportCommand (file renamed PublishCommand.cs -> ExportCommand.cs) and update the CLI command name and all user-facing strings from "publish" to "export". Update Program to register ExportCommand, adjust related help/error messages and option descriptions, and update the CliToolbarActionContext comment to reference the export toolbar placement. Functionality is unchanged aside from renaming and messaging.

Use verbatim string literals for F# directives

Use C# verbatim string literals (@"...") when composing F# script directives to avoid escaping issues with Windows paths. Updated #r, #load and #I generation to produce @"path" in FSharpKernel.cs, NuGetReferenceProcessor.cs and ScriptDirectiveProcessor.cs so embedded file paths are handled correctly.

Bundle blazor.web.js in CI and simplify csproj

Add CI steps (verso-ci and verso-release) to extract blazor.web.js from the .NET 8 Components.Endpoints.dll into src/Verso.Cli/bin/Release/net8.0/wwwroot/_framework so the CLI tool bundles the script even when the runtime rolls forward. Update Verso.Cli.csproj: change RollForward from LatestMajor to Major, remove the RoslynCodeTaskFactory inline extraction fallback, and replace it with a simpler target that copies the NuGet-cached blazor.web.js into the output path and emits a warning if the file is not found. These changes ensure the tool package contains the required blazor.web.js for "verso serve" across runtime roll-forwards.

Stop propagation on toolbar dropdown popups

Remove tabindex and @onfocusout from the dropdown container elements and add @OnClick:stopPropagation to the dropdown popup divs in Toolbar.razor. This prevents clicks inside the popup (layout and theme popups) from bubbling and inadvertently closing the dropdown, fixing issues where interacting with popup items caused them to immediately dismiss.

CLI: bundle static assets and improve UI interactions

Add global-tool support and several UX fixes across the Blazor frontend and CLI.

- README: document the CLI (verso serve/run/convert/info) and usage examples.
- BlazorHostBuilder: detect when the static web assets manifest is invalid (global tool scenarios) and fall back to Production mode; serve bundled wwwroot via PhysicalFileProvider when appropriate; added HasValidStaticWebAssetsManifest helper.
- Verso.Cli.csproj: include a build target to package Verso.Blazor and Verso.Blazor.Shared wwwroot and Blazor framework JS into the tool package so the server can serve static files when installed as a global tool.
- ServeCommand: defer opening the browser until the app has started (ApplicationStarted) to avoid race conditions with Kestrel binding.
- JS (parameters-interop.js): improve Enter-key handling to confirm adds and commit parameter value edits immediately (including preventing default for non-checkbox inputs and sending parameter-update interactions).
- CSS: add small spacing (gap: 4px) for boolean parameter controls.
- Cell.razor: add @key to HTML output containers to force Blazor to recreate DOM when output objects change, avoiding removeChild errors with interactive elements.
- ParametersCellRenderer: show "required" label text next to the required checkbox in add/edit rows.

These changes make the CLI-installable server reliable when run as a global tool and improve parameter editing and rich-output rendering in the Blazor UI.

Add cell drag-and-drop UI and interop

Introduce client-side cell drag-and-drop support and wire it into Blazor pages. Added a new cell-drag-interop.js (Shared and Blazor/wwwroot) implementing ghost dragging, auto-scroll, and drop indicator, plus CSS for drag visuals and cursors. Updated NotebookPage.razor (WASM and Components) to mark cell wrappers with data-cell-index, register the interop via a DotNetObjectReference, add a JSInvokable OnCellDragDrop handler to move cells, and dispose the ref on teardown. Also include the new script in WASM index.html, App.razor, and the VS Code Blazor editor provider so the interop is loaded in all hosts.

Spawn per-notebook host and set working dir

Start a dedicated HostProcess per notebook webview and pass a working directory to the host when opening a notebook.

Changes:
- Add WorkingDir to C# NotebookOpenParams and set Environment.CurrentDirectory in NotebookHandler so F# __SOURCE_DIRECTORY__ and relative paths resolve against the notebook.
- Update VS Code protocol to include optional workingDir in NotebookOpenParams.
- Blazor editor: spawn a HostProcess per webview, manage hosts in a map, start/stop hosts with the panel lifecycle, and send workingDir when calling notebook/open.
- Pass the per-notebook HostProcess into BlazorBridge instead of a single global host and update save/revert/backup flows to use the correct host.
- Remove the single global host startup from the extension activation; BlazorEditorProvider now receives hostDllPath and creates hosts as needed.

This ensures notebook file-relative behavior is correct and isolates host processes per notebook.

Rename CredentialResolver to PlaceholderResolver

Rename the CredentialResolver helper and its tests to PlaceholderResolver, updating all usages (including SqlConnectMagicCommand) to the new name. Add a doc comment clarifying ResolveVariable resolves $var: placeholders in any string and return (resolved, error). Add a unit test covering empty variable values returning an error, and update tests to reference the renamed class. Adjust redaction and resolution calls accordingly.