v1.19.0 — Reliable recommendations, chained-scenario traceability, .deb packaging fixes

Reliability fixes

• mode_conseille (pre-flight configuration advice) is now filtered to
  successful diagnostic runs only — a diagnostic interrupted mid-way (WAF
  block, timeout, crash) can no longer feed a recommendation to a later call.

New capability

• Chained-scenario traceability (chainage): when a scenario uses
  declencher_scenario, the journal now records the full call tree
  (scenario, depth, action_start, action_end) alongside the flattened
  action list. The root CLI reader (journal.py) renders it as an indented
  tree. Absent on any run without chaining — purely additive.

Debian package fixes

• postinst now creates /opt/diwall/references/ — missing since the
  package's introduction, this caused watch.py --sauver-reference to fail
  with a permission error on a fresh install.
• postinst now sets the execute bit on shot.py/watch.py/rpa.py/
  journal.py — watch.py invokes shot.py as a direct subprocess and
  failed with a permission error without it.
• Both caught and fixed via a real install/remove cycle on this release.

Documentation

• Clarified: etat (the deterministic operational verdict) is declarative,
  never a gate — no verb dispatcher checks pret_a_agir before running an
  action.
• New decision rule for --ignorer-waf: only after an independent,
  non-mutating check confirms the page is actually usable.
• Documented the guide-read lock's cooperative-nature limit (a model already
  holding a valid token can pass it without rereading the guide) rather than
  hardening it.
• Reference-safe assertion guidance for --replay-verifier/
  monitor-verifier.sh: assert structure, not volatile values (timestamps,
  counters, session tokens).
• Zero-delay guidance for min_action_delay_ms on local development targets
  — the shipped default (800 ms) protects an unconfigured first run against
  the public internet, not a doctrine of slowness.
• New docs/ACCESS_OBSERVATIONS.md: a neutral, dated log of real access
  outcomes.
• Three previously undocumented watch.py flags now documented:
  --prompt, --heatmap-tile, --sortie-json.
• GUIDE.md title and wording no longer single out "human" operators.

Tooling (git source only, not packaged)

• scripts/verifier-coherence.sh: static check that documentation notice
  versions stay in sync with the index table, and that every CLI flag is
  documented somewhere under docs/.