feat: session work column enhancements — Files Changed editing + project-wide Preview with PDF and TeX support - #737

…rt (#725)

- Add extension-side recursive directory scan (preview_file_tree.ts)
  with RENDERABLE_EXTENSIONS filter, hidden-dir/node_modules skip
- Add preview-file-tree bridge message: extension pushes filtered file
  list on app-ready and on refresh request from webview
- Add app-side state store (amicode-preview-file-tree.ts) with SolidJS
  signals for project files, project root, and optional environment
- Wire bridge: chat_bridge.ts handles preview-file-tree-request via
  registered command; extension.ts pushPreviewFileTree on app-ready
- Transform session-preview-tab.tsx: when project tree available, show
  FileTreeV2 in static mode with search/filter input; when bound to
  a Research Environment, show env files below a labeled divider with
  colored pill (same 8-color palette as sidebar); preserve session-
  touched .md flat list as no-project fallback
- 14 unit tests for scan filter, 5 for state store, all green

…or parsing (#729)

- Add tex_support.ts: detectTexEngine (latexmk > pdflatex > xelatex >
  lualatex detection chain), discoverMainFile (\documentclass scan),
  parseTexErrors (! errors + file:line:msg patterns), compileTeX
  (subprocess with AbortController cancellation)
- Extend WorkspaceProjectEntry with tex? field (available, engine,
  mainFile) for bridge push enrichment
- Wire TeX engine detection at extension startup (async, non-blocking)
- Add tex-compile-request bridge handler + amicode.texCompile command:
  cancels in-flight compile, pushes status via tex-compile-status
- 12 unit tests: engine detection shape, main file discovery (5 cases),
  error parsing (4 cases)

Sync: PDF viewer (#727), PlainEditor CM6 extension map (#728),
preview-content-area with real renderers, SyncTeX parser (#730),
preview-file-tree state store, session-ui legacy-modes dep.

Merges all 6 slices:
- #725: Project-wide file tree with search + environment support
- #726: Renderer dispatch (markdown, PDF, images, CodeMirror)
- #727: PDF rendering (pdfjs-dist, zoom, scroll preservation)
- #728: CodeMirror 6 editor (line numbers, syntax highlighting, auto-save)
- #729: TeX compilation pipeline (detection, Build button, error parsing)
- #730: SyncTeX forward search (minimal parser + lookup)

Closes #725, closes #726, closes #727, closes #728, closes #729, closes #730

…wlists (#725/#729)

The VS Code webview relay in chat_panel.ts has explicit allowlists for
which bridge message kinds are forwarded between the extension and the
iframe. The four new message kinds were missing, causing the extension's
pushPreviewFileTree to be silently dropped by the relay — the app never
received the file list, so hasProjectTree() stayed false and the legacy
'No markdown files' empty state showed instead of the project file tree.

Added to iframe→extension (lane 1): preview-file-tree-request,
tex-compile-request. Added to extension→iframe (lane 2):
preview-file-tree, tex-compile-status. Both relay renderers (renderHtml
+ renderTransitionHtml) updated.

5 structural tests verifying each kind appears in both renderers.

pushPreviewFileTree required a research project (research-project.toml)
in the VS Code workspace — dev workspaces like amicode itself got no
file tree at all, falling back to the legacy session-touched .md list.

Extract pickPreviewProject() into preview_file_tree.ts: prefers a
research project when one exists, falls back to the first dev project
otherwise. Environment resolution stays gated to research projects
(dev projects never have a bound environment).

The scanner already skips node_modules, .git, dist, build, and hidden
dirs, so dev-repo scans are safe and bounded.

7 new tests: 5 unit tests for pickPreviewProject priority logic,
2 structural tests verifying extension.ts uses the new function.