Align coverage docs with toggle-advisory semantics #ci-float

Follow-up review caught three stale doc spots that still asserted the old
toggle-mandatory / ptype-blind behavior after the gate semantics changed:

- zkf_coverage.py module docstring: --gate is per-PR line-only (not "historical"),
  --full is line+branch mandatory with toggle advisory (not "line, branch, OR toggle").
- zkf_coverage.py HTML report empty-state: "every line and branch covered (toggle
  advisory)" instead of implying toggle is gated.
- Makefile: the verify-float-extended block said "line+branch+toggle coverage
  closure"; toggle is advisory, so "line+branch coverage closure (toggle advisory)".

Docs/comments only; no logic or RTL change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: pavel-kirienko

Makefile

@@ -103,7 +103,7 @@ coverage-float-gate:
 
 ## Deep-tier-only extended sweep: fills the parity/relation/WINT parameter gaps (correctness, Icarus) and
 ## drives a curated set of exhaustive small-format Verilator runs into build/float/verilator-toggle for
-## full line+branch+toggle coverage closure. Per-PR verify/verify-float never invoke this.
+## line+branch coverage closure (toggle reported advisory). Per-PR verify/verify-float never invoke this.
 verify-float-extended: library
 	@rm -rf build/float/icarus-ext build/float/verilator-toggle
 	@$(FLOAT_PYTEST) -m deep

float/tb/zkf_coverage.py

@@ -11,9 +11,10 @@
 
 Gating modes:
 
-  * ``--gate``  : fail on any uncovered executable LINE (historical behaviour, used by per-PR CI).
-  * ``--full``  : fail on any uncovered line, branch, OR toggle point. Used by the deep tier
-                  (``coverage-float-gate-full``).
+  * ``--gate``  : per-PR tier (used by ``coverage-float-gate``) - fail on any uncovered LINE point only.
+                  Branch is gated by ``--full``; toggle coverage is advisory and never gated here.
+  * ``--full``  : deep tier (used by ``coverage-float-gate-full``) - fail on any uncovered LINE or BRANCH
+                  point. TOGGLE coverage is reported as advisory but is never fatal.
 
 Verilator coverage points are keyed per parameterisation AND per hierarchy instance, but the *net
 name* (``o`` field) is parameter- and instance-independent. We merge points by
@@ -232,7 +233,7 @@ def bar(st: Stats) -> str:
     detail = (
         "<h2>Uncovered points</h2><table><thead><tr><th>Source</th><th>Kind</th><th>Line</th>"
         "<th>Net / block</th></tr></thead><tbody>" + "\n".join(detail_rows) + "</tbody></table>"
-        if detail_rows else "<h2>Uncovered points</h2><p class='good'>None — every line, branch, and toggle covered.</p>"
+        if detail_rows else "<h2>Uncovered points</h2><p class='good'>None — every line and branch covered (toggle advisory).</p>"
     )
 
     genhtml_link = ("<p><a href='lcov/index.html'>Detailed line drill-down (genhtml) &rarr;</a></p>"