docs: update the first local Flatpak build's time and size

AGENTS.template.md and project.cpp gave the first run flatpak as about
25 minutes on a 56-core machine and its state as about 2 GB, figures
written on 2026-10-06, before lldb and the Vulkan and SPIR-V modules
were in the manifest. A first run of this commit's manifest, in a fresh
worktree, took 30 min 36 s with 56 CPU threads, 14 min of it for LLVM
with lldb, and left build/flatpak at 4.1 GB, 3.3 GB of it state/.

The figures become those, and the line on later runs says that they
rebuild only the crafter-build module while the manifest is unchanged.

project.cpp

@@ -16,7 +16,8 @@ namespace {
     struct FlatpakPaths {
         fs::path manifest;
         // flatpak-builder's downloads, ccache and per-module cache. The
-        // LLVM build lives here: about 2 GB, and 25 minutes to rebuild.
+        // LLVM build lives here: about 3 GB in all after a first run,
+        // which takes about 30 minutes with 56 CPU threads.
         fs::path state;
         // The OSTree repo the build is exported to; `install` reads it.
         fs::path repo;