feat(nip46): show user's kind-0 profile (name, about, NIP-05) after Amber login

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Bug Description

The user's bug report (second part): "it doesn't give a success message on the actual device, it needs to give a success message there and also show the profile of the person when it's working in HOOT."

After a successful NIP-46 QR pairing, the home screen showed only the raw 16-char pubkey prefix (m.publicKey[:16]). There was no code anywhere in the codebase that fetched the user's kind-0 (NIP-01 profile metadata) event, and no UI element to render the name / about / picture / NIP-05 from one.

Fix

Wires the kind-0 profile fetch end-to-end from session → TUI → home screen:

1. nip46.Session.FetchProfile(ctx, userPubKey) — new method that queries the same relay connections opened by ConnectRelays for a kind-0 event authored by the user. No extra dial cost (amortises the QR-pairing latency). 6-second timeout so a dead relay doesn't block the TUI login flow. Returns (nil, nil) — not an error — when the user has no kind-0 event, so the caller falls back to the npub display without raising an error toast.

2. hoot.go:OnCheckQR — after GetPublicKey returns, calls FetchProfile and returns the result alongside the pubkey. Successful fetch is cached in the existing cache.profiles table with 24h TTL.

3. tui.qrSuccessMsg — now carries the profile alongside the pubkey. The success message becomes "Logged in as " when a name is available; falls back to "Logged in via Amber!" otherwise.

4. tui.viewHome — when currentProfileAbout or currentProfileNIP05 is set, renders them under the title in dim style. The NIP-05 gets a ✓ prefix to communicate verification status at a glance.

How to Verify

1. go run . and pick "Scan QR with Amber".
2. After Amber approves, the home screen shows "🦉 Hoot - " with the about line + NIP-05 below (if you've set them in Amber).
3. Run with a profile-store user (nsec login) — the existing currentProfileName is used unchanged, no regression.
4. Run with a user who has no kind-0 event — the home screen falls back to the 16-char pubkey prefix.

Test Plan

• TestProfileMetadataJSONRoundTrip — pins the wire format
• TestProfileMetadataOmitsEmptyFields — pins the omit-empty contract
• TestFetchProfileRejectsEmptyPubKey — input-validation guard
• TestFetchProfileRejectsNoRelays — "called too early" guard
• TestProfileNameIsRenderable — covers ASCII/emoji/unicode/whitespace/markup cases
• Existing tui tests updated to the new OnCheckQR signature
• Full suite green (go test ./...)
• go vet ./... clean
• Manual verification of the four scenarios above

Risk Assessment

Low. The change is purely additive on the success path:

• New fields on the TUI Model (currentProfileAbout, currentProfileNIP05) are only set by the new code path, and only displayed when non-empty.
• The success message change ("Logged in as X" vs "Logged in via Amber!") is purely cosmetic — the underlying loggedIn/publicKey state is unchanged.
• FetchProfile failures are non-fatal by design — they degrade gracefully to npub display, identical to the pre-change behaviour.
• The cache write is best-effort (_ =); a cache failure doesn't break sign-in.

The TUI's OnCheckQR signature changed (func() (string, error) → func() (string, *nip46.ProfileMetadata, error)). All four test files using SetCallbacks were updated; no other callers exist outside hoot.go.