fbt: reproducible manifest builds & improvements (#1801)

* fbt: reproducible manifest builds, less rebuild on small updates; scripts: assets: using timestamp from commandline af available
* fbt: added app import validation for launch_app & single app build targets
* fbt: COMSTR for app imports validation
* docs: minor fixes
* docs: markdown fix
* vscode: comments for RTOS startup

Co-authored-by: あく <alleteam@gmail.com>

assets/SConscript

@@ -1,8 +1,11 @@
 Import("env")
 
+from fbt.version import get_git_commit_unix_timestamp
+
 assetsenv = env.Clone(
     tools=["fbt_assets"],
     FW_LIB_NAME="assets",
+    GIT_UNIX_TIMESTAMP=get_git_commit_unix_timestamp(),
 )
 assetsenv.ApplyLibFlags()
 
@@ -90,10 +93,11 @@ if assetsenv["IS_BASE_FIRMWARE"]:
         "#/assets/resources/Manifest",
         assetsenv.GlobRecursive("*", "resources", exclude="Manifest"),
         action=Action(
-            '${PYTHON3} "${ASSETS_COMPILER}" manifest "${TARGET.dir.posix}"',
+            '${PYTHON3} "${ASSETS_COMPILER}" manifest "${TARGET.dir.posix}" --timestamp=${GIT_UNIX_TIMESTAMP}',
             "${RESMANIFESTCOMSTR}",
         ),
     )
+    assetsenv.Precious(resources)
     assetsenv.AlwaysBuild(resources)
     assetsenv.Clean(
         resources,