Fnos packaging (#2524)

* feat(packaging): add fnOS FPK packaging and CI workflow

Add packaging/fnos/ shell (manifest, lifecycle cmd scripts, install/
upgrade/uninstall wizards, desktop entry, EULA) plus in-repo build
script. A release now auto-builds langbot-<tag>-fnos.fpk via
.github/workflows/build-fnos-fpk.yaml, uploaded to the release assets.

* ci(fnos): skip release upload on manual dispatch

github.event.release.tag_name is empty when triggered via
workflow_dispatch, causing 'gh release upload' to fail with
'requires at least 2 arg(s)'. Restrict the step to release events.

* ci(fnos): normalize release asset name

Strip a trailing -fnos from the tag-derived version before appending
the suffix, avoiding langbot-<v>-fnos-fnos.fpk when the tag itself
already carries -fnos.

* ci(fnos): use release tag version for auto build, manifest for manual

Auto build (release/tag) reads version from tag like other release
workflows; build.sh strips the v prefix when injecting into manifest.
Manual dispatch falls back to the version maintained in manifest.

* feat(fnos): add post-install deployment notice to install wizard

Last wizard step now informs users that first startup takes about
5-10 minutes for dependency setup before the web UI is ready.

* docs(fnos): add packaging directory README

* refactor(fnos): rename app from ai.langbot to langbot

Rename appname, desktop entry, data share, build artifacts, and all
references from ai.langbot to langbot across packaging files.

---------

Co-authored-by: dadachann <185672915+dadachann@users.noreply.github.com>

packaging/fnos/cmd/config_callback

@@ -0,0 +1,6 @@
+#!/bin/bash
+# cmd/config_callback - post-config hook
+# Applies wizard-provided settings (e.g. Node.js version) that cmd/main reads.
+# Nothing to persist currently; cmd/main reads wizard_node_version at runtime.
+
+exit 0