Feed events and @mentions

Feed events (idea #127)

Events → + New invite creates an event with a title, optional date/time

and location, and details. Pick friends and followers to invite — they get

an in-app notification and can RSVP (Going / Interested / Can't make

it) from the notification or the event page.

Inviting someone also posts an event card to your feed with an RSVP link,

so fans can pile on. The guest list on the event page shows every RSVP.

If an invitee never answers, they sit in the "invited" column — no email,

no spam, just the notification.

Type `@Venue Name` or `@Band Name` in any wall or feed post and the post

is saved with a tappable chip linking to that band or venue. Matching is

by full name against real bands and venues — a name only links when it

unambiguously matches, and the venue you played is always included on

auto-generated gig posts (see gig-auto-posts.md).

Mention chips render on the feed, profile walls, and band walls.

Feed posts have a category — General, Gigs, Wanted, Lessons — chosen

when you post. The feed has filter tabs at the top so you can see just

gig announcements or just wanted ads. Category labels appear on each post.

the exact band/venue name, and make sure the name is followed by a

space or punctuation — "Jamie" won't link if you typed "JamieX".

notification when they next visit; there's no email push, so mention it

in person too.