Vamooses Neighbors

### Added
- Favourites: click the star icon on any owned plot, friend house, or guild
  house to pin it to the top of its list. Favourited rows render in a
  collapsible "Favourites" section above regular results, persisted across
  reloads per account.
- Custom groups: named buckets for organising houses. Right-click any row (or
  its star) and pick a group from the context menu to add/remove, or use the
  "Groups" header button on Friends/Guild to create, rename, and delete groups.
  Grouped houses render in their own collapsible sections above Favourites.
- Default "Empty" group (config option, default on): a renamable,
  non-deletable starter group that doubles as an auto-container for empty
  plots on the Neighborhood sub-tab. Renames stick; empty plots follow the
  bucket wherever you rename it to. Toggle in Config > "Keep a default group"
  to disable or delete it entirely.
- Faction sorting: header icon button on Friends and Guild sub-tabs splits the
  list into Alliance and Horde sections (persisted in config, default off).
  Faction split is hidden on Neighborhood since neighborhoods are single-
  faction -- instead, the neighborhood name now displays the faction atlas
  inline (Alliance/Horde icon next to the zone name).
- BattleTag display on BNet friend houses: friend rows show
  "CharName (User#1234)" so it's easier to tell whose alt is whose. Guild
  members who are also BNet friends pick up the tag too; same-realm neighbours
  match when the char name is unambiguous. (thanks Happymoon)
- Combined right-click context menu: one tidy popup with the Favourite
  toggle, per-group checkmarks (accent swatch when a member), a Manage-groups
  shortcut, and -- on the Neighborhood sub-tab with Manager mode on -- the tag
  picker inline below a divider.

### Changed
- House row layout gained a small star affordance on the left edge of each
  owned plot. Empty plots are unchanged.
- Close buttons now use atlas icons (`common-icon-redx`) on both the main
  panel and the Groups popup; delete/rename per group row use
  `common-icon-delete` and `UI-RefreshButton` with tooltips; "New group" uses
  `communities-icon-addgroupplus`.
- Section header rows (groups, favourites, faction) paint with a lighter
  scrim so they read clearly above regular rows on every theme.

### Fixed
- Endeavor progress bar no longer resets to "Loading endeavor..." shortly
  after login. The BNet/guild initiative scan was triggering a nil
  `NEIGHBORHOOD_INITIATIVE_UPDATED` payload right after restoring the viewing
  neighborhood; that no longer clobbers the last-known initiative. The player
  leaving a neighborhood still clears it via the existing RefreshPlots path.
- `/reload` and character relog no longer wrongly report "House keys expired"
  or trigger a full re-scan. VN now persists `GetSessionTime()` at scan
  completion and compares it on the next load; since GetSessionTime resets
  only on a full WoW client restart, we can distinguish cold-launch
  (houseGUIDs invalidated, re-scan needed) from any in-client reload/relog
  (houseGUIDs still valid, reuse cache).