[#841] Display "{human}'s AI Writer" via ERC-8004 owner + FID lookup

[realproject7]

Parent Epic: #841

Summary

When an ERC-8004 agent writes a story, display the human owner'''s identity instead of a bare wallet address. Show "{farcaster_name}'''s AI Writer" everywhere the writer identity appears.

How it Works

```
Story writer: 0xdABF... (OWS wallet)
→ Is this an ERC-8004 agent? Check users.agent_id
→ Yes → Look up owner: users.agent_owner = 0x4d68...
→ Does owner have FID? Check users table or Neynar API
→ Yes, FID 8106 → "project7'''s AI Writer"
```

Tasks

1. Cache Owner FID

When agent is registered/indexed:

• `users` table already has `agent_owner` column
• After indexing agent registration, also look up the owner'''s Farcaster data via Neynar
• Cache owner'''s `fid`, `display_name`, `pfp_url` in the agent'''s user row or a separate lookup

2. WriterIdentity Component

Modify `src/components/WriterIdentity.tsx` (or `WriterIdentityClient.tsx`):

• Current: shows wallet address or Farcaster name for the writer
• New: if `writer_type === "agent"` AND `agent_owner` has a Farcaster identity:
  • Show: {owner_display_name}'''s AI Writer with owner'''s Farcaster avatar
  • Smaller text below: Agent #{agent_id} · {agent_name}
• Fallback: if owner has no FID, show: AI Writer #{agent_id} (current behavior)

3. Profile Page

On the agent'''s profile page (`/profile/{owsWallet}`):

• Add "Operated by" section:
  • Owner'''s Farcaster avatar + display name
  • Link to owner'''s profile page
  • Badge: "ERC-8004 Verified" (on-chain binding)
• Keep existing agent stats below

4. Story Cards

On StoryCard component where writer is shown:

• Same logic: if agent with owner FID → "{name}'''s AI Writer"
• Small AI badge icon next to the name

5. Story Detail Header

On the storyline page header:

• Writer section: "{name}'''s AI Writer" with link to both profiles
• Or: "Written by {agent_name} · Owned by {owner_name}"

Data Flow

• `users.agent_owner` → already populated on registration
• `users.fid` (for owner) → already fetched via Neynar on onboard
• Just need to JOIN: agent user → owner user → owner'''s Farcaster data

Acceptance Criteria

• WriterIdentity shows "{human}'''s AI Writer" when agent has owner with FID
• Profile page shows "Operated by" section with owner info
• Story cards show human-linked AI writer name
• Falls back to plain agent display when owner has no FID
• All data sourced from on-chain ERC-8004 (not off-chain hack)