feat: v0.7.0 files pane: browse, preview, diff, Claude's edits

- devdesk attach --fs-list/--fs-read/--git-status/--git-show/--asset
  (libexec/devdesk-files.sh), confined to the session folder.
- The state hook records files Claude edits (Edit/Write/MultiEdit/
  NotebookEdit) for the Changes tab's "C" badge; rename/end carry it.
- Files pane: folders, CodeMirror read-only view, sanitized markdown preview
  in a sandboxed iframe with inlined relative images, images, Changes tab with
  line counts and diff against HEAD, "→ Claude" @path, resizable split.
- The editor bundle ships as /usr/share/devdesk/assets/editor.js, is fetched
  over ttyd on first use, verified against the page's SHA-256 and cached in
  IndexedDB.
- Fix: the state hook's field split collapsed empty fields.

Closes #19

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Makefile

@@ -8,7 +8,7 @@ SHAREDIR   := $(PREFIX)/share/devdesk
 TTYD_ARCH  ?= x86_64
 
 SHELL_SCRIPTS := bin/devdesk $(wildcard libexec/devdesk-*) scripts/fetch-ttyd.sh debian/devdesk.postinst debian/devdesk.postrm
-WEB_SOURCES   := web/build.mjs web/index.template.html web/styles.css $(wildcard web/src/*.js) \
+WEB_SOURCES   := web/build.mjs web/index.template.html web/styles.css $(wildcard web/src/*.js) $(wildcard web/editor/*.js) \
                  vendor/web_template/base.css debian/changelog
 
 .PHONY: all lint test install clean sync-template
@@ -26,7 +26,7 @@ build/ttyd: vendor/ttyd/VERSION vendor/ttyd/SHA256SUMS scripts/fetch-ttyd.sh
 	@touch $@
 
 lint: node_modules/.package-lock.json
-	npx eslint --max-warnings 0 --ext .js,.mjs web/src web/build.mjs tests/protocol.test.mjs
+	npx eslint --max-warnings 0 --ext .js,.mjs web/src web/editor web/build.mjs tests/protocol.test.mjs
 	shellcheck -x $(SHELL_SCRIPTS)
 	jq empty share/claude-settings.json
 
@@ -41,8 +41,11 @@ install: all
 	install -m 0755 libexec/devdesk-picker libexec/devdesk-claude-run libexec/devdesk-session-hook \
 		libexec/devdesk-tmux-ready libexec/devdesk-serve libexec/devdesk-statusline \
 		libexec/devdesk-deploy libexec/devdesk-state-hook libexec/devdesk-notify-matrix $(DESTDIR)$(LIBDIR)/
+	install -m 0644 libexec/devdesk-files.sh $(DESTDIR)$(LIBDIR)/devdesk-files.sh
 	install -m 0755 build/ttyd $(DESTDIR)$(LIBDIR)/bin/ttyd
 	install -m 0644 dist/index.html share/tmux.conf share/claude-settings.json $(DESTDIR)$(SHAREDIR)/
+	install -d $(DESTDIR)$(SHAREDIR)/assets
+	install -m 0644 dist/assets/editor.js $(DESTDIR)$(SHAREDIR)/assets/editor.js
 	install -m 0644 etc/env $(DESTDIR)$(SYSCONFDIR)/devdesk/env
 
 clean: