Docs: bring the documentation in line with the code

- Demo docs replaced by the screencast docs (single source of truth): the
  legacy demo-session.sh/demo-record.py and the v0.9 renderer were removed
  instead of being kept as a second convention.
- feature-matrix: stale 'M2-in-progress' vocabulary gone; the rows the 15
  gates prove now say VERIFIED-in-VM and name the gate; af-to is now an
  explicit non-goal row (INET6 0 in this build).
- guide: the queues/divert/pflog sections described a state that no longer
  exists (priq-only, divert dropping packets, pflog logging nothing); they
  now describe the shipped behaviour.
- vm-lab: the 15 real gates with what each proves, 15/15 green, and the
  pf0 -> cli/srv/gw2 ssh setup the screencasts rely on.
- install/build: pdivert and pflogd are built and ported (docs said
  otherwise); module object list now includes hfsc.c, fq_codel.c, pfk_pflog.c;
  the screencast pipeline is an optional build stage.
- pf-guide: the 'M2 scope only' framing is gone; honest gaps listed.
- caveats: three new sections about the screencast pipeline (MiniMax video
  generation blocked by the account tier, narration as a separate track, a
  video frame is not a verdict).
- porting-notes: what the recording taught us.
- README/README.pt-BR: status, milestones, layout and video section updated.

All internal doc links verified.

docs/en/screencast.md

@@ -1,6 +1,6 @@
 # Screencasts / Videos da demonstracao
 
-> PT-BR: [docs/pt-BR/screencast.md](pt-BR/screencast.md) · EN: this page
+> PT-BR: [docs/pt-BR/screencast.md](../pt-BR/screencast.md) · EN: this page
 
 Sete videos por idioma, com **narracao com voz feminina** (MiniMax),
 **legendas queimadas**, **diagrama de rede do lab** e um **filme completo**
@@ -52,7 +52,7 @@ Etapas individuais:
 ```sh
 python3 scripts/screencast/make_audio.py --lang pt      # audio MiniMax
 python3 scripts/screencast/record.py --plan scripts/screencast/plans/04-roteamento.json \\
-        --out out/screencast/caps/04-roteamento.cast --pace
+        --out out/screencast/caps/04-roteamento.cast --pace --ensure-pf
 python3 scripts/screencast/assemble.py --phase 04-roteamento --lang pt
 python3 scripts/screencast/join.py --lang pt
 ```