Crt, Ripple and Glitch take a level, 0 to 3, tunable at run time

Coordinator's request: `Crt 0..3` (likewise Ripple, Glitch), 0 off, `on`
the default level 2 (the polished rewrite), `off` and a bare word as
before. The level is one uniform (pardesLevel, beside pardesOpaque in the
prefix's own block); each pass picks its constants by it. Level 3 is at
least as strong as the old effects, measured as pixels changed by more
than 8 in a channel against a plain frame: Crt 18.3% (old 17.4%), Ripple
11.1% (9.5%), Glitch 9.3% a frame (8.1%); Glitch's level raises how often
it bursts as well as how hard. Config and ctl report `Crt 2` / `Crt off`.

Shared files touched: ninep/ctl.zig (the report line). Not touched:
pardes.zig, Messages.zig, mouse.zig, gui.zig, detached/*.

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