Add nested location group; remove address, link, and sniffing

[edalzell]

Breaking 7.0 cut for #190.

location becomes a declared group for the physical place; online_url stays a sibling (already shipped in 6.2). Nested coords ship here — not as a top-level 6.x field (#194 superseded) — so 6→7 upgrades don't need a separate coords migration.

Warning

Blocked on transformstudios/prime#834 for Prime sites. Duplicate location handles collapse silently. Events must not ship into Prime blueprints until Prime renames its group.

Fieldset

Location section on events::event (already has online_url from #193):

location:                    # group
  name: text                 # localizable — ICS LOCATION (plain desc or address)
  coordinates:               # nested group
    latitude / longitude     # float
online_url:                  # sibling — already declared

No top-level address, link, or top-level coordinates.

Resolution

src/Types/Event.php:

• icsLocation() → string location.name, else fallback to online_url when empty
• GEO from location.coordinates (reuse hasValidCoordinates())
• eventUrl() / optionally rename → icsUrl(): only online_url (drop link + URL-location sniff)
• delete icsAddress(); stop reading top-level address / coordinates / string location
• read via get(); if location isn't a group or name isn't a non-empty string, skip — never fatal

Mapping

Event	LOCATION:	URL:	GEO:
Physical only	location.name	—	location.coordinates
Online only	online_url	online_url	—
Hybrid	location.name	online_url	location.coordinates

Tests

TDD first.

• each mapping row, all four download routes
• declared nested coords → GEO:; partial/non-numeric still safe
• foreign/non-group location ignored (collapse Only pass string addresses to ICS downloads #184-style group tests into this)
• address / link / top-level coordinates / URL sniff no longer read
• a URL string in location.name is a location, not a join URL

Docs

• rewrite ICS table + fieldset docs for the nested contract
• location + online_url independent/combinable
• start 7.0 upgrade notes (migrator details in Add update script migrating location fields to 7.0 #196)

Branch

feature/location-field off main. Stacks after 6.2 content already on main.

Part of #190.