Finish #309: lib/gen citations, the 31 unregistered probe_ files, dead shot_ scripts, drifted line citations

[mtklein]

Left from #309 (build/attempts/wt/retire-manual/deferred_edits.txt):

• tools/tests/lib/ot6.lua: 25 comment lines citing deleted probes (lines listed in deferred_edits.txt), and gen_narshe_battle.lua:50 (narshedescentlab) -- deferred while Kefka at Narshe is a coin flip for the route's fighter (5/7 first attempts); lab it #257 edits those files; apply after it merges.
• 31 probe_*.lua files without @Manual are exempt from registration by name; the TESTING.md policy applies to them too (instrument, or delete with findings in the commit).
• shot_mines.lua and shot_final.lua boot mines_chase.mss, which no generator makes.
• Line-number citations have drifted: gen_rapids.lua:85 and gen_scenario.lua:147 cite 'metrics_battle.lua:110'; mechanics-coverage.md's file:line citations likewise. Prefer symbol names over line numbers.
• The clock-based left/right walker drifts out of its encounter pool #306's list names probe_swdtech, now deleted.