[PR #3] Revised Actor Discovery Alignment

[aaronjae22]

Closes #259

This PR rebuilds Actor-based portability discovery to the revised LOLA draft.

Per LOLA §4.1: "The portability authorization endpoint MAY be the same as or different from other OAuth endpoints."

Field	Purpose
oauthAuthorizationEndpoint	The actor's general-purpose OAuth authorization endpoint — standard ActivityPub OAuth (normal login/authorization, etc.).
oauthMigrationEndpoint	The portability-specific authorization endpoint — where a destination server starts the LOLA account-migration OAuth flow and requests the activitypub_account_portability scope. This is the field LOLA §4.2 makes a MUST.

It replaces the top-level accountPortabilityOauth field with a public endpoints object (oauthMigrationEndpoint + parallel oauthAuthorizationEndpoint).

Also corrects the scope-gated migration object to {outbox, content, following, blocked} on dedicated actors/<pk>/migration/... routes, and keeps liked/followers as regular Actor collections.

Public / unauthenticated — GET /api/actors/1/

Expected result

{
  "@context": ["https://www.w3.org/ns/activitystreams", "https://purl.archive.org/socialweb/blocked", "https://swicg.github.io/activitypub-data-portability/lola"],
  "type": "Person",
  "id": "http://localhost:8000/api/actors/1",
  "preferredUsername": "alice",
  "name": "alice",
  "inbox": "http://localhost:8000/api/actors/1/inbox",
  "previously": [],
  "endpoints": {
    "oauthAuthorizationEndpoint": "http://localhost:8000/oauth/authorize/",
    "oauthMigrationEndpoint": "http://localhost:8000/oauth/authorize/"
  }
}

Authenticated with portability token — GET /api/actors/1/ (adds the gated block)

Expected result

{
  "outbox":    "http://localhost:8000/api/actors/1/outbox",
  "following": "http://localhost:8000/api/actors/1/following",
  "followers": "http://localhost:8000/api/actors/1/followers",
  "liked":     "http://localhost:8000/api/actors/1/liked",
  "blocked":   "http://localhost:8000/api/actors/1/blocked",
  "migration": {
    "outbox":    "http://localhost:8000/api/actors/1/migration/outbox",
    "content":   "http://localhost:8000/api/actors/1/migration/content",
    "following": "http://localhost:8000/api/actors/1/migration/following",
    "blocked":   "http://localhost:8000/api/actors/1/migration/blocked"
  }
}