Add observation search and filtering, and user location filtering

[newmanw]

Summary

Adds a search bar to the observation list and filter dialogs for observations and user locations.

• Observation search: search observations by keyword from the list toolbar.
• Observation filter: filter by time range, team or member, attachments, favorites, important, and per-field conditions.
• Location filter: filter people by time range and team or member.

Both lists show their active filters, result count and paging, and recover from failed searches with a retry. The filters also apply to the map, and the export page reuses the keyword and condition filters.

Changes

Client

• New observation filter dialog, user location filter dialog and search bar, replacing the old filter component. They are standalone, use control flow and signals with OnPush, and follow Material 3.
• EventService and FilterService drive the map, list page and locations from triggers with per-fetch teardown, so switching events or destroying the service drops late responses instead of applying them.
• The member filter takes an event id, teams and an initial filter, owns its chips after init and clears them when the event changes.
• Flagging as important and favoriting update the list immediately instead of waiting for the next poll.
• Typed the map layers, user locations and observation entities shared by these components, and removed the unused follow inputs on the people list.

Server

• Exports keep both the keyword and the condition when both are sent, and drop the filter when neither is.
• Favorite and important updates populate the same user fields as the read path, so responses match what the list expects.
• Documented the known team-scoping gap in resolveUserIsAnyOf.

Known gaps

• Filter by form is not in the new observation dialog. The old "Forms" chips are gone. The condition builder needs a field, and the server search has no form-presence filter. This will be restored in a separate PR.
• Malformed conditions are silently ignored by the export and search endpoints.
• resolveUserIsAnyOf does not check that a team id belongs to the event (documented in code).
• Hand-rolled listener arrays in EventService and MapService remain. Replacing them with observables is planned for a later PR.