feat(apps): permission manager equips apps (manifest+consent+decisions in /system), launches via init w/ file grant; shell unprivileged (/home); install/apps/allow/revoke; revoke stops running app; app-image tool; counter app

disk/home/docs/shell.txt

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+The shell runs an app by asking the permission manager, passing along
+the terminal as its output and a read-only grant to the current folder:
+all the shell has to give. The permission manager adds what the app's
+manifest asks for and you allowed, and runs it. Ctrl+C stops it.
+
+You decide what each app may use: `install <folder>` asks you, `apps`
+shows what each may use, `allow` and `revoke` change it (revoking from
+a running app stops it).
+
+Built-ins: help, echo, clear, cd, pwd, apps, install, allow, revoke.

disk/home/readme.txt

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+Welcome to k-os.
+
+Every program here is an app that runs with only the capabilities it
+was given: this file reached your screen because the shell handed `cat`
+the terminal and read-only access to this folder, and nothing else.
+
+Try:  ls        cd docs        cat shell.txt        cat ../readme.txt
+      apps      snake (q quits)      sleep 30, then Ctrl+C
+      install inbox/counter, then counter, counter