fix(time): konfigurierbare Fach-Zeitzone statt UTC/OS-Local fuer alle Datumsangaben

Lieferbericht zeigte UTC (08.09. 22:54 statt 09.09. 00:54): renderer.dt()
formatierte DateTime<Utc> ohne Umrechnung. Weitere Stellen hingen an
chrono::Local (OS-Zone des Hosts) bzw. hardcodiertem 'Europe/Berlin'.

Neu: server.timezone (IANA, Default Europe/Berlin, chrono-tz) und
durchgaengig UTC-Instant -> konfigurierte Zone:
- Lieferbericht: alle Zeitstempel (Abgeschlossen, Notizen, Scans, erzeugt am)
- Belegansicht (fmt_datetime)
- ERP-Rueckschreibung delivered_at (Wanduhrzeit)
- 'heute'-Ableitung: /me/tours, /dev/resync, /admin/import-erp,
  Import-Cron + Startup-Catch-up
- Completion-Repo: AT TIME ZONE als Bind-Param statt Literal

Speicherung bleibt UTC (TIMESTAMPTZ / DateTime<Utc>) - nur Anzeige und
Kalendertag-Ableitung nutzen die Zone.

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

Cargo.lock

@@ -427,6 +427,17 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "chrono-tz"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a6139a8597ed92cf816dfb33f5dd6cf0bb93a6adc938f11039f371bc5bcd26c3"
+dependencies = [
+ "chrono",
+ "phf",
+ "serde",
+]
+
 [[package]]
 name = "color_quant"
 version = "1.1.0"
@@ -1018,6 +1029,7 @@ dependencies = [
  "askama",
  "axum",
  "chrono",
+ "chrono-tz",
  "holzleitner-application",
  "holzleitner-domain",
  "holzleitner-infrastructure",
@@ -1045,6 +1057,7 @@ version = "0.1.0"
 dependencies = [
  "async-trait",
  "chrono",
+ "chrono-tz",
  "holzleitner-domain",
  "imagesize",
  "serde",
@@ -1070,6 +1083,7 @@ version = "0.1.0"
 dependencies = [
  "async-trait",
  "chrono",
+ "chrono-tz",
  "holzleitner-application",
  "holzleitner-domain",
  "image",
@@ -1931,6 +1945,24 @@ version = "2.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
+[[package]]
+name = "phf"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "913273894cec178f401a31ec4b656318d95473527be05c0752cc41cdc32be8b7"
+dependencies = [
+ "phf_shared",
+]
+
+[[package]]
+name = "phf_shared"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06005508882fb681fd97892ecff4b7fd0fee13ef1aa569f8695dae7ab9099981"
+dependencies = [
+ "siphasher",
+]
+
 [[package]]
 name = "pin-project-lite"
 version = "0.2.17"
@@ -2777,6 +2809,12 @@ dependencies = [
  "time",
 ]
 
+[[package]]
+name = "siphasher"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ee5873ec9cce0195efcb7a4e9507a04cd49aec9c83d0389df45b1ef7ba2e649"
+
 [[package]]
 name = "slab"
 version = "0.4.12"