feat: shelldocs dev + build — hot-reload watcher and static-site publisher

[Shewart]

Summary

Fills in the two remaining CLI commands: shelldocs dev (thin wrapper around dotnet watch run with markdown in the watch set) and shelldocs build (dotnet publish -c Release + static-hosting post-processing for GH Pages / Cloudflare / S3). Both follow the InitCommand pattern — small orchestrator class per command, wired into Program.cs.

Last CLI feature branch before chore/release-0.1.0-alpha.

What's in it

src/ShellDocs.CLI/Commands/DevCommand.cs

• Locates the .csproj in --dir (default cwd), errors cleanly if missing.
• Spawns dotnet watch --project <csproj> --non-interactive run --urls http://localhost:<port> with inherited stdio so the user sees dotnet's output live.
• Forwards Ctrl+C to the child process tree so shutdown is clean.
• Returns the child's exit code.

src/ShellDocs.CLI/Commands/BuildCommand.cs

• Runs dotnet publish -c Release -o obj/shelldocs-publish (scratch dir under the project's obj/).
• Detects publish shape: if wwwroot/ exists inside the publish output → Blazor WASM (static site). If not → Blazor Server (whole publish dir is the payload, needs a .NET host).
• Copies the appropriate source to --output, wiping the target first so stale files never linger between builds.
• Two post-processing flags:
  • --base-href "/my-repo/" — rewrites <base href="..." /> in index.html (needed for GH Pages subpath deployments). Regex handles single-quote, double-quote, and no-quote variants; case-insensitive.
  • --spa-fallback — copies index.html → 404.html so GH Pages returns the SPA shell for unknown paths instead of a real 404 (standard client-routing trick).
• Prints Spectre summary showing project, output path, kind (static vs server), and the applied post-processing steps.

src/ShellDocs.CLI/Program.cs — swaps both placeholder handlers for real dispatches. Adds --dir on both commands to match init. build gains --base-href and --spa-fallback options.

tests/ShellDocs.Tests/BuildCommandTests.cs — 7 unit tests covering the deterministic post-processing helpers (via reflection since they're internal). Doesn't shell out to dotnet publish — that's an integration surface I verified by hand.

• RewriteBaseHref — 4 quote-variant cases all rewrite correctly
• RewriteBaseHref leaves surrounding markup untouched
• CopyDirectory recursively copies nested files preserving relative paths
• CopyDirectory overwrites existing files in the destination

Full suite: 85 passing (was 78, +7).

Notes

• dev doesn't add extra file globs to the watch set directly — dotnet-watch >= 8 already picks up razor + css + js. For markdown watching, the CLI relies on the consumer's csproj declaring <Watch Include="content/**/*.md" /> (something shelldocs init can add in a follow-up). MVP works fine because ShellDocs re-reads markdown files at render time.
• build uses obj/shelldocs-publish as scratch rather than the default bin/Release/net10.0/publish so we don't collide with a user's own publish artifacts. Cleaned up after the copy either way.
• Search index generation deferred — the roadmap item mentioned "search stub for now" but there's nothing to stub yet. Adding an empty search-index.json at build time would be dead weight until the runtime consumes it.

Test plan

• dotnet build shelldocs.slnx — clean
• dotnet test shelldocs.slnx — 85 passing
• shelldocs dev --help and shelldocs build --help — options render, defaults correct