fix(tipping): validate NWC URI before saving; add HTTP timeouts on LNURL

[oth-body]

Summary

Two defense-in-depth fixes on the Lightning tipping path (hoot -nwc, hoot -tip).

What this fixes

1. NWC URI was saved to disk without validation

Pre-fix: hoot -nwc garbage silently wrote "garbage" to nwc.txt (mode 0600, but the connection secret was the only auth — if the file ever leaked to a filesystem that strips permissions, the connection was wide open). The user got no error and no indication that the URI was malformed.

Post-fix: a new validateNWCURI(uri) helper runs before any disk write. It rejects:

• empty input
• wrong URL scheme (must be nostr+walletconnect://)
• missing wallet pubkey in the URL authority
• missing ?relay= query parameter
• missing ?secret= query parameter

The check is intentionally permissive — any future NIP-47 extension field passes through unchanged — but it catches the cases that would have failed later in a less-actionable way.

2. resolveLud16 and fetchLightningInvoice had no HTTP timeout

Pre-fix: both used the default http.Get with no context and no timeout. If the LNURL endpoint hangs (slow wallet, network partition, malicious response that never closes the stream), hoot -tip would freeze forever waiting for the response. This is the kind of failure that turns a one-shot CLI invocation into a manual kill.

Post-fix: explicit http.Client{Timeout: 10*time.Second} for both calls. The LUD-16 spec recommends a 10s timeout for lnurlp responses, and 10s is short enough to not annoy users on slow networks but long enough to not abort legitimate slow responses.

Tests

nwc_validation_test.go (new, 7 table-driven cases):

URI	Expected
""	error: must not be empty
https://example.com	error: scheme must be nostr+walletconnect
nostr+walletconnect://?relay=wss://r&secret=abc	error: missing pubkey
nostr+walletconnect://pubkey?secret=abc	error: missing relay
nostr+walletconnect://pubkey?relay=wss://r	error: missing secret
nostr+walletconnect://pubkey123?relay=wss://...&secret=hexsecret	accepted
valid + extra params (lud16=...)	accepted

Also updated hoot_test.go TestNWCParsing — the old version pinned the bug (passed "invalid-uri" and expected "saved successfully"). New version uses a properly-formatted URI and asserts the save path still works end-to-end.

Conflict check

• fix(hoot): dedupe defaultRelays; surface NWC payment uncertainty #61 (silent-failures-hoot): zero overlap — fix(hoot): dedupe defaultRelays; surface NWC payment uncertainty #61 modified defaultRelays, generateProfileID, payInvoiceNWC. This PR modifies the NWC helpers and resolveLud16/fetchLightningInvoice.
• fix(hoot): publishNote counts successes; error path no longer skips defers #62 (publish-error-surfacing): zero overlap — fix(hoot): publishNote counts successes; error path no longer skips defers #62 added publishNote() and rewired the main() publish loop. This PR touches the tipping path.