Add file badges, menu icons, LSP diagnostics, robust compaction

- Files in chat: preview with type/size badges and file name; attachment chips
- Menu and settings tabs with icons
- Heatmap: distinct colour for empty hours, hourly labels
- Context chip shows used/total tokens (e.g. 221k/240k) plus percent
- LSP client: diagnostics appended to edit/write results and a diagnostics tool
  (typescript-language-server, pyright, rust-analyzer, gopls, clangd; sandboxed)
- Compaction summarizes a plain transcript and retries once on empty output
- files/stat endpoint

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

config.example.toml

@@ -182,6 +182,7 @@ bash_output = "allow"
 kill_shell = "allow"
 web_fetch = "ask"
 web_search = "allow"
+diagnostics = "allow"
 browser_snapshot = "allow"
 image_compare = "allow"
 generate_image = "ask"   # costs money per image
@@ -299,6 +300,23 @@ url = ""
 api_key = ""
 
 
+# -----------------------------------------------------------------------------
+#  Language servers (diagnostics after edits, tool "diagnostics")
+# -----------------------------------------------------------------------------
+#  Built in: rust (rust-analyzer), typescript (typescript-language-server),
+#  python (pyright-langserver), go (gopls), c (clangd) – used when installed.
+#  TypeScript and Python servers ship with the image. Servers run in the
+#  user's sandbox and stop after 15 minutes without use.
+# -----------------------------------------------------------------------------
+[lsp]
+enabled = true
+# Add or override a server:
+# [lsp.servers.zig]
+# command = "zls"
+# extensions = ["zig"]
+# root_markers = ["build.zig"]
+
+
 # -----------------------------------------------------------------------------
 #  Sandbox
 # -----------------------------------------------------------------------------