feat: add web layer (internal/web) and wire it into main.go

Routing, html/template layout/content pattern, and the Pre-Publish
check flow: POST /pruefen runs extraction (Stufe 1) then rules.Evaluate
(Stufe 2) and renders the result as an htmx fragment. Nothing is
persisted yet — that's the next step (wiring internal/store in).

The needsClarification case is rendered explicitly as a request for
more information rather than "no findings", matching the core
principle. Every result carries the legal-advice disclaimer required by
CLAUDE.md's guardrails.

Server depends on a narrow Extractor interface rather than *extract.
Client directly, so tests inject a fake instead of calling the real API
— internal/web's test suite never touches the network. htmx is vendored
locally (internal/web/static/htmx.min.js) instead of loaded from a CDN,
keeping the UI usable without runtime internet access.

cmd/deklarix/main.go now wires all of this together: reads
ANTHROPIC_API_KEY (required) and RULES_DIR (default "rules"), builds
the extract client and loads the rule set, and serves web.Server instead
of the old inline health-only mux.

This exposed the same crash-loop risk fixed earlier for DATABASE_URL:
postinst's start guard only checked DATABASE_URL, so a fresh install
would now crash-loop on a missing ANTHROPIC_API_KEY instead. The guard
checks both. scripts/build.sh also now ships rules/*.yaml into the .deb
under /usr/share/deklarix/rules (not a conffile — rules are updated via
the release pipeline, never hand-edited on a server), and
deklarix.env.example points RULES_DIR there by default.

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

packaging/etc/deklarix/deklarix.env.example

@@ -5,11 +5,14 @@
 
 PORT=8080
 
-# Pflicht — der Dienst startet nicht ohne gültige DATABASE_URL. Auskommentiert
-# lassen, bis eine echte Postgres-Verbindung eingetragen ist: postinst prüft
-# genau diese Zeile, um den Dienst nicht blind in eine Restart-Schleife gegen
-# einen Platzhalter-Host laufen zu lassen.
-#DATABASE_URL=postgres://user:password@host:5432/deklarix?sslmode=require
+# Wo internal/rules die YAML-Regeln findet — vom .deb-Paket nach
+# /usr/share/deklarix/rules installiert (siehe scripts/build.sh).
+RULES_DIR=/usr/share/deklarix/rules
 
-# Für internal/extract (Claude-API-Extraktion), sobald angebunden.
+# Pflicht — der Dienst startet nicht ohne gültige DATABASE_URL und
+# ANTHROPIC_API_KEY. Beide auskommentiert lassen, bis echte Werte
+# eingetragen sind: postinst prüft genau diese beiden Zeilen, um den
+# Dienst nicht blind in eine Restart-Schleife gegen Platzhalter laufen
+# zu lassen.
+#DATABASE_URL=postgres://user:password@host:5432/deklarix?sslmode=require
 #ANTHROPIC_API_KEY=