fix(chat): recall the current session's prompts by default; tidy the six merged PRs

Input history (#3035) shipped with "All projects" as the default scope and
only recorded prompts sent after the upgrade, so ArrowUp showed other
sessions' prompts and, once switched to "Current session", nothing at all.
Default to the current session and merge the visible transcript's prompts
with the persisted bucket. Existing sessions recall as they did before
#3035, while new prompts keep their attachments and stay recallable after
a revert hides them from the transcript.

Cleanup across #1855, #2297, #3072, #3178, #3035 and #3135: drop the
duplicate poll guards in the file content poller, the zod schema the
VS Code package cannot depend on, a copied file-URL helper and stray
whitespace; move the Enter-to-send strings into the settings namespace;
document OPENCHAMBER_CHATS_DIR, resolve the chats root once on the server
and warm it alongside the other bootstrap calls.

packages/web/bin/lib/cli-startup.js

@@ -313,8 +313,7 @@ function getCurrentUsername() {
 // when the user has lingering enabled. Detect it so `startup enable` can warn
 // that the service may otherwise stop on logout. Returns null when the state
 // cannot be determined (no username, loginctl unavailable, or odd output).
-function getUserLingerEnabled(username) {
-  const user = typeof username === 'string' && username.length > 0 ? username : getCurrentUsername();
+function getUserLingerEnabled(user) {
   if (!user) {
     return null;
   }