docs: update architecture docs and diagrams for recent changes

ARCHITECTURE.md:
- Directory structure: add middleware/requireAuth.js and favicon assets
- §4.1: remove CORS from middleware list
- §4.2: all proxy routes now auth-required via requireAuth; add
  middleware description
- §6: cookie payload corrected (no token); document secure+sameSite
- §7: add emby:users cache key (60s TTL)
- §8: Download Object table: userTag → allTags/matchedUserTag/tagBadges
- §9 POST /login: document cookie security attributes
- §10: add Tag Badge Rendering section; remove hardcoded line count

Diagrams:
- class-server.puml: add requireAuth middleware module; update
  dashboard.js methods (extractAllTags, extractUserTag w/ username,
  buildTagBadges, getEmbyUsers); add TagBadge value class; add auth
  relationships for all proxy routes
- class-data.puml: Download Object userTag → allTags/matchedUserTag/
  tagBadges; add TagBadge class; remove token from Session Cookie
- seq-auth.puml: cookie payload no longer contains token; add
  secure/sameSite note
- component.puml: remove CORS component; add requireAuth; consolidate
  Emby connection to show tag badge + user-summary usage
- activity-matching.puml: update to extractAllTags/extractUserTag
  (with username); showAll uses hasAnyTag; tagBadges built from
  embyUserMap; add Emby user fetch step; update legend
- seq-dashboard.puml: add emby:users cache lookup / Emby fetch for
  showAll; update matching groups to show tag classification; add
  tag badge rendering note on renderDownloads()

docs/diagrams/class-data.puml

@@ -153,7 +153,9 @@ package "sofarr Internal Models" {
     + movieName : string | null
     + episodeInfo : object | null
     + movieInfo : object | null
-    + userTag : string
+    + allTags : string[]
+    + matchedUserTag : string | null
+    + tagBadges : TagBadge[] | undefined
     + importIssues : string[] | null
     + downloadPath : string | null
     + targetPath : string | null
@@ -170,6 +172,11 @@ package "sofarr Internal Models" {
     + completedAt : string
   }
 
+  class "TagBadge" as tagbadge <<value>> {
+    + label : string
+    + matchedUser : string | null
+  }
+
   class "API Response\n/user-downloads" as apir {
     + user : string
     + isAdmin : boolean
@@ -201,7 +208,7 @@ package "sofarr Internal Models" {
     + id : string
     + name : string
     + isAdmin : boolean
-    + token : string
+    ' Note: Emby AccessToken intentionally excluded
   }
 
   apir *-- dl
@@ -215,7 +222,9 @@ sabh ..> dl : matched &\ntransformed
 qbt ..> dl : mapTorrentToDownload()
 ss ..> dl : coverArt, seriesName,\npath, tags
 rm ..> dl : coverArt, movieName,\npath, tags
-tag ..> dl : userTag resolution
+tag ..> dl : allTags / matchedUserTag
 eu ..> cookie : login creates
+eu ..> tagbadge : buildTagBadges()
+dl *-- tagbadge : tagBadges[]
 
 @enduml