docs: update README + api docs + architecture for v2.0.0 feed

README
  - Mention social feed in the one-line description and feature bullets
  - Add relay + feed endpoint tables to the API overview (was
    previously empty on messaging)
  - List media/ package in the repo structure

docs/api/
  - New docs/api/feed.md: full reference for /feed/publish, fetch,
    stats, view, author, timeline, trending, foryou, hashtag; all
    on-chain CREATE_POST / DELETE_POST / FOLLOW / LIKE payloads;
    fee economics; server-side scrubbing contract.
  - docs/api/relay.md rewritten: /relay/broadcast is now the primary
    E2E path with a complete envelope schema; /relay/send kept but
    flagged ⚠ NOT E2E; DELETE /relay/inbox/{id} documented with the
    new Ed25519 signed-auth body.
  - docs/api/README.md index: added feed.md row.

docs/architecture.md
  - L2 Transport layer description updated to include the feed
    mailbox alongside the 1:1 relay mailbox.
  - New "Социальная лента (v2.0.0)" section right after the 1:1
    message flow: ASCII diagram of publish + on-chain commit +
    timeline fetch, economic summary, metadata-scrub summary.

docs/node/README.md
  - Removed stale chan:/chan-member: keys from the BadgerDB schema
    reference; replaced with the v2.0.0 feed keys (post:,
    postbyauthor:, follow:, followin:, like:, likecount:).

docs/update-system.md
  - Example features[] array updated to match the actual node output
    (channels_v1 removed, feed_v2 / media_scrub / relay_broadcast added).

Node feature flags
  - api_well_known_version.go: dropped channels_v1 tag (the
    /api/channels/:id endpoint was removed in the feed refactor);
    added feed_v2, media_scrub, relay_broadcast so clients can
    feature-detect the v2.0.0 surface.
  - Comment example updated channels_v2/v1 → feed_v3/v2.

Client
  - CLIENT_REQUIRED_FEATURES expanded to include the v2.0.0 feature
    flags the client now depends on (feed_v2, media_scrub,
    relay_broadcast); checkNodeVersion() will flag older nodes as
    unsupported and surface an upgrade prompt.

All 7 Go test packages green; tsc --noEmit clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

node/api_well_known_version.go

@@ -12,7 +12,7 @@
 // returned forever (even if the implementation moves around internally). The
 // client uses them as "is this feature here or not?", not "what version is
 // this feature at?". Versioning a feature is done by shipping a new tag
-// (e.g. "channels_v2" alongside "channels_v1" for a deprecation window).
+// (e.g. "feed_v3" alongside "feed_v2" for a deprecation window).
 //
 // Response shape:
 //
@@ -55,15 +55,17 @@ const ProtocolVersion = 1
 // a breaking successor (e.g. `channels_v1`, not `channels`).
 var nodeFeatures = []string{
 	"access_token",              // DCHAIN_API_TOKEN gating on writes (+ optional reads)
-	"channels_v1",               // /api/channels/:id + /members with X25519 enrichment
 	"chain_id",                  // /api/network-info returns chain_id
 	"contract_logs",             // /api/contract/:id/logs endpoint
 	"fan_out",                   // client-side per-recipient envelope sealing
+	"feed_v2",                   // social feed: posts, likes, follows, timeline, trending, for-you
 	"identity_registry",         // /api/identity/:pub returns X25519 pub + relay hints
+	"media_scrub",               // mandatory EXIF/GPS strip on /feed/publish
 	"native_username_registry",  // native:username_registry contract
 	"onboarding_api",            // /api/network-info for joiner bootstrap
 	"payment_channels",          // off-chain payment channel open/close
-	"relay_mailbox",             // /relay/send + /relay/inbox
+	"relay_broadcast",           // /relay/broadcast (E2E envelope publish)
+	"relay_mailbox",             // /relay/inbox (read), /relay/send (legacy non-E2E)
 	"ws_submit_tx",              // WebSocket submit_tx op
 }