docs: split README into distributed docs, fix stale/broken content

README had drifted: an unresolved merge-conflict marker left over from a
past edit, a directory-structure diagram that no longer matches the repo
(/internal/site, /internal/domains/platforms/tiktok - actual layout is
server/, domains/, etc per AGENTS.md), and a duplicated dev-workflow blurb
that AGENTS.md already documents more accurately.

Splits the roadmap checklist out to ROADMAP.md and the Etsy API compliance
checklist to domains/platforms/etsy/COMPLIANCE.md (next to the code it
governs, where someone touching that integration will actually look for
it) instead of burying both in one large README. README itself becomes a
short front door with a "Where things live" index up top, since scattering
docs across files only helps if there's an obvious map to them.

Moves the CQRS/event-sourcing architecture note into AGENTS.md's
Architecture section (with a new domains/raw_events bullet) rather than
leaving it as prose in README, since AGENTS.md is the maintained
engineering reference and that's where a reader would already be looking
for how the domains are structured.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

AGENTS.md

@@ -117,6 +117,12 @@ against the live API doesn't exist yet.
   ORM/repository layer. Looking to loosely follow CQRS: writes go through
   domain `Store` methods, reads are mostly separate query methods on the
   same `Store`.
+- `domains/raw_events` - the [event-sourcing](https://martinfowler.com/eaaDev/EventSourcing.html)
+  store: `Save` appends an `Event`, `LoadEventsForStore` replays a
+  platform+store's series. Other domains (`reports`,
+  `domains/accounts/mocks.go`) read from views/queries that project over
+  this event series rather than mutating their own standalone state. See
+  also the [CQRS](https://martinfowler.com/bliki/CQRS.html) note above.
 - `domains/accounts/mocks.go` - the mock-platform simulation layer:
   `CreateMockShop`, `CreateMockListing`, `SaveNewMockSale` /
   `SaveNewMockRefund` / `SaveNewMockInventoryReset`, etc. These are the