fix: knowledge retrieval accuracy and remaining brand/PoC leaks in procedure docs

- Fix the demo knowledge provider's tokenizer: a plain [a-z0-9]+ regex silently
  dropped accented characters, splitting French words like "véhicule" into "v" +
  "hicule" and mangling retrieval for nearly every French query. Now matches the
  Latin-1 accented range too.
- Reweight section scoring so the body match (the actual substance of a section)
  outranks a heading/title match (a shallow structural hint) rather than the reverse
  -- confirmed via the brief's exact validation question that the old weighting
  misranked the damage procedure behind a topically-adjacent document in all three
  languages (nl-BE: a checkout section; en-GB/fr-BE: the return procedure), purely
  because a generic word like "vehicle"/"voertuig" happened to sit in a heading/title.
- Remove leftover "MobilityOps" and "PoC" mentions from 5 English and 4 NL/FR
  procedure documents -- knowledge-base prose is visible UI content and was missed by
  the earlier rebrand.
- Add regression tests: the brief's exact NL/EN/FR damage question must ground on the
  damage procedure as the *primary* source (not just appear in the top 3), and no
  procedure file may contain "MobilityOps" or "PoC".

151 backend tests, Ruff, mypy green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

knowledge/procedures/fr-BE/03-damage-handling.md

@@ -14,7 +14,7 @@ Lorsqu'un véhicule revient avec des dommages visibles ou signalés, marquez le
 
 ## 2. Preuves
 
-Enregistrez au moins quatre photographies dans le système d'inspection source : côté affecté en entier, gros plan, contexte plus large et plaque d'immatriculation. Fleet Ops ne peut stocker que la référence à cette preuve dans ce PoC.
+Enregistrez au moins quatre photographies dans le système d'inspection source : côté affecté en entier, gros plan, contexte plus large et plaque d'immatriculation. Fleet Ops ne peut stocker que la référence à cette preuve dans cet environnement de démo.
 
 ## 3. Escalade