Add fediverse social features: followers/following lists, actor timelines

Adds get_followers_paginated and get_actor_timeline to FederationService
protocol + SQL implementation + stubs. Includes accumulated federation
changes: models, DTOs, delivery handler, webfinger, inline publishing,
widget nav templates, and migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

contracts/dtos.py

@@ -187,3 +187,68 @@ class APAnchorDTO:
     ots_proof_cid: str | None = None
     confirmed_at: datetime | None = None
     bitcoin_txid: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class RemoteActorDTO:
+    id: int
+    actor_url: str
+    inbox_url: str
+    preferred_username: str
+    domain: str
+    display_name: str | None = None
+    summary: str | None = None
+    icon_url: str | None = None
+    shared_inbox_url: str | None = None
+    public_key_pem: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class RemotePostDTO:
+    id: int
+    remote_actor_id: int
+    object_id: str
+    content: str
+    summary: str | None = None
+    url: str | None = None
+    attachments: list[dict] = field(default_factory=list)
+    tags: list[dict] = field(default_factory=list)
+    published: datetime | None = None
+    actor: RemoteActorDTO | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class TimelineItemDTO:
+    id: str  # composite key for cursor pagination
+    post_type: str  # "local" | "remote" | "boost"
+    content: str  # HTML
+    published: datetime
+    actor_name: str
+    actor_username: str
+    object_id: str | None = None
+    summary: str | None = None
+    url: str | None = None
+    attachments: list[dict] = field(default_factory=list)
+    tags: list[dict] = field(default_factory=list)
+    actor_domain: str | None = None  # None = local
+    actor_icon: str | None = None
+    actor_url: str | None = None
+    boosted_by: str | None = None
+    like_count: int = 0
+    boost_count: int = 0
+    liked_by_me: bool = False
+    boosted_by_me: bool = False
+    author_inbox: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class NotificationDTO:
+    id: int
+    notification_type: str  # follow/like/boost/mention/reply
+    from_actor_name: str
+    from_actor_username: str
+    created_at: datetime
+    read: bool
+    from_actor_domain: str | None = None
+    from_actor_icon: str | None = None
+    target_content_preview: str | None = None