20260923 - One Send link button for the node claim

[Purple10101]

Replaces the claim section's Save and Send again with a single Send link button. The other half of Unclaim & Reclaim Fail, with offworldlabs/retina-telemetry#22.

Why

On jonathan-node-1 the owner released the node from the dashboard, then neither button produced a link.

Save was the trap. Saving an address the node already held wrote an identical file, so retina-telemetry could not see the press and sent nothing. After a release the address never changes, so Save could never ask again. Send again reached the node but was a resend, and a release clears the address a resend mails to. retina-telemetry#22 fixes that half.

What changes

Every press of Send link stamps send_requested_at beside the address. One press is one email, whatever state the claim is in, and nothing is sent without a press. The node still decides the call, as before:

Press on	retina-telemetry sends
A new or changed address	PUT /nodes/claim (the stamp beside it counts as answered)
The same address, server still holds it (declined, pending)	POST /nodes/claim/resend
The same address on a released node	PUT /nodes/claim (needs retina-telemetry#22)

• An empty box on Send removes the record, as an empty Save did. It never unclaims the node.
• The button is disabled while the node reads Owned, with a hint to release from the dashboard. A resend is refused there, and a new address would be offering somebody else's node.
• /set-up/claim loses its resend flag and the requested key in its answer. The page was their only caller.
• save_telemetry_claim loses request_send and no longer carries an old stamp forward, since there are no plain saves left for that to protect.

Order of release

Either order is safe. With this and a retina-telemetry that lacks #22, the only case still broken is the released node, exactly as today. #22 without this fixes Send again but leaves Save as a silent no-op after a release.

Verification

• ruff check ., pre-commit run --all-files and the full pytest suite (942) pass, run on a clean checkout of origin/main plus this change.
• New tests: the same address sent again moves the stamp, and the button is disabled when Owned and enabled when not.
• Not yet run on a node.

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