A community based topic aggregation platform built on atproto

fix(lexicon): correct subscription subject field to use DID format

Change subscription lexicon subject field format from "at-identifier"
to "did" for consistency and correctness:

Before:
- format: "at-identifier" (accepts DIDs or handles)
- description: "DID or handle of the community"

After:
- format: "did" (only accepts DIDs)
- description: "DID of the community being subscribed to"

Rationale:
1. Matches block.json pattern (which correctly uses "did" format)
2. Aligns with service layer implementation (only supports DIDs)
3. Follows atProto convention: "subject" field references entities by DID
4. Prevents invalid handle values in federated records

This ensures subscription records are properly validated and compatible
with the broader atProto ecosystem.

Changed files
+2 -2
internal
atproto
lexicon
social
coves
community
+2 -2
internal/atproto/lexicon/social/coves/community/subscription.json
···
"properties": {
"subject": {
"type": "string",
-
"format": "at-identifier",
-
"description": "DID or handle of the community being subscribed to"
},
"createdAt": {
"type": "string",
···
"properties": {
"subject": {
"type": "string",
+
"format": "did",
+
"description": "DID of the community being subscribed to"
},
"createdAt": {
"type": "string",