feat: VS Code extension for inline annotations

[backnotprop]

Summary

• Adds apps/vscode-extension/ — a VS Code extension for inline annotation markers using start/end <!-- @plannotator NNNN: text --> comments
• Right-click context menu: "Add Annotation" and "Export Annotations"
• Keyboard shortcut: Cmd+Alt+P (Mac) / Ctrl+Alt+P (others)
• Auto-incrementing 4-digit IDs (0001, 0002, ...) with multi-line marker support
• Export produces Plan Feedback markdown format, copied to clipboard
• Configurable prefix via plannotator.annotationPrefix setting
• Zero runtime dependencies, esbuild bundled to CJS
• Adds dev:vscode and build:vscode root scripts

Closes #91

Test plan

• Open apps/vscode-extension/ in VS Code, press F5 to launch Extension Development Host
• Place cursor on a line, right-click → "Plannotator: Add Annotation"
• Verify <!-- @plannotator 0001: --> inserted above with cursor positioned for typing
• Select multiple lines → Add Annotation → verify start/end markers wrap the selection
• Add 3 annotations → verify IDs increment: 0001, 0002, 0003
• Test keyboard shortcut Cmd+Alt+P
• Right-click → "Plannotator: Export Annotations" → verify Plan Feedback markdown copied to clipboard
• Verify bun run build:vscode works from repo root

Publishing checklist

Assets

• Extension icon — 256x256px PNG (no SVG), referenced as "icon" in package.json
• apps/vscode-extension/README.md — this is what shows on the marketplace listing
• apps/vscode-extension/CHANGELOG.md (optional but recommended)
• Screenshots/GIFs for the README showing add annotation + export flow

package.json updates

• Bump version (currently 0.0.1 — decide: sync with root or independent versioning)
• Add "icon": "icon.png"
• Add "homepage" URL
• Add "bugs" URL
• Add "galleryBanner" (optional, customizes marketplace page colors)
• Review "keywords" for discoverability

Publisher account

• Create Azure DevOps org at https://dev.azure.com/ (if not already)
• Create publisher at https://marketplace.visualstudio.com/manage with ID backnotprop
• Generate Personal Access Token (PAT) with Marketplace (Manage) scope
• Store PAT as GitHub Secret: VSCE_PAT

CI/CD — extend .github/workflows/release.yml

• Add vscode-publish job (parallel to existing npm-publish)
• Build: bun run build:vscode
• Package: npx @vscode/vsce package --no-dependencies (already in scripts)
• Publish: npx @vscode/vsce publish -p $VSCE_PAT
• Attach .vsix to GitHub Release as artifact
• Respect existing DRY_RUN flag for dry-run mode
• Decide: publish on every v* tag, or separate vscode-v* tags

Pre-publish validation

• vsce package succeeds with no warnings
• All README images use HTTPS URLs (no SVG except trusted badge providers)
• .vscodeignore excludes src/, node_modules/, config files (already done)
• Extension activates and works from packaged .vsix (install via Extensions → Install from VSIX)

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