capture: close batch-quarantine silence, 0-byte asymmetry, and round-two doc overclaims

Batch captures now name the retained-render folder once instead of nothing; Auto/Manual tail modes refuse a 0-byte render like None does; VERIFICATION.md steps 1-3 no longer invite a false conclusion; docs/comments no longer overclaim.

docs/PLAN.md

@@ -2128,8 +2128,8 @@ full-extent case runs literally unchanged code, keeping the byte-identity regres
 floor structural and the fix cheap to revert if the override inference proves wrong.
 Also landed: a transient isolation guard (cutting `B_MAINSEND` on direct folder
 children, muting receives) so an item capture stays true to item scope, and a
-post-render frame-count gate (±1 tolerance, tail-None only) that refuses and self-cleans
-a widened render. New modules `core/capture/render_window`, `core/capture/track_topology`,
+post-render frame-count gate (±1 tolerance, tail-None only) that refuses a widened
+render and retains it outside the bank for diagnosis rather than deleting it. New modules `core/capture/render_window`, `core/capture/track_topology`,
 `shell/capture/render_selection`, `shell/capture/render_isolation`. The whole fix rests
 on the unverified inference that REAPER's selected-tracks render source overrides
 custom time bounds — Ψ-W3-T1 (below) now also depends on it. **DAW-verification