Keep showing a guest link's URL so it can be copied again

The URL was shown once, in a box under the create button, and then gone: only
a hash of the token was stored, so the app genuinely could not produce it a
second time. Lose the message you sent the sitter and the only way back was to
mint a new link — which strands whoever is already holding the old one.

Settings now lists every live link with its URL and a Copy button, so re-sending
one is just copying it again.

That means keeping the token rather than only its hash, and it is worth being
plain about the trade. It is not the trade you would make for a password, which
the user has probably reused, or a session token, which grants everything
indefinitely. A guest link grants a strict subset of what the same database
already holds in plaintext, expires on a date the owner picked, and can be
revoked in one tap — so an attacker who can read puppy.db gains very little by
also being able to open it as a guest. The lookup column stays a hash and
remains the key redeem matches against; the secret sits in a new column beside
it, which also keeps the migration additive.

Links created before this have an empty secret. They keep working and stay
revocable — the migration touches nothing but the new column — and the list
says why their URL is missing rather than rendering a broken one.

The two tests that asserted the old contract now assert the new one: a listing
hands back a secret that really opens the link, and the lookup column is still
a hash. Added one for the legacy row, since "still works, just cannot be shown"
is the part a future change is most likely to break quietly.

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-09-07", "text": "Guest links can be copied whenever you want. Settings → Guest access now shows each live link's URL next to it with a Copy button, instead of showing it once when you created it and never again. If you lose the message you sent, or want to pass the same link to someone else, you can just take it again rather than making a new one and leaving whoever already had the old one locked out. Links you made before this change can't be shown — only a scrambled form of those was kept — so revoke one and create a fresh one if you need its URL back" },
   { "date": "2026-09-07", "text": "Fixed buttons that were meant to be hidden but showed anyway. A guest opening an entry the owner logged saw Delete and Save on it — they never worked (the server refuses the change) but they had no business being there. The same fault had been quietly affecting three other things for a while: the 🌳 pedigree button appeared before you had set a pedigree ID, “Send a test notification” appeared when reminders weren't available, and the exercise dialog offered Delete while you were adding a new exercise rather than editing one. One styling rule was overriding every one of them" },
   { "date": "2026-09-07", "text": "A day can now be left out of the stats. Open the day, tap “⊘ Not counted” next to the overview heading, and it stops feeding the charts and averages — useful when someone else had the puppy and the record is thinner than the day really was, so it isn't fair to count it. Nothing is deleted or hidden: the day's own overview, history and sleep & wake list are exactly as they were, just dimmed and labelled, and you can switch it back at any time. In the day-by-day charts the day keeps its place but is drawn as a hatch instead of a bar, so a deliberate gap can't be misread as a day the puppy barely slept. Weigh-ins and notes still count wherever they fall — those are facts you recorded, not behaviour a sparse day distorts — so the weight curve and the Notes log are untouched. The Timing panel throws away gaps that reach across a skipped day rather than measuring them, which would otherwise turn two normal days into one enormous fake gap" },
   { "date": "2026-09-06", "text": "You can hand someone temporary access without giving them your login. Settings → “Guest access” creates a link — say who it's for and pick the last day it should work — and whoever opens it lands straight in the app on your dog, able to log events and read all the history and charts. They can't change your entries: a guest may fix up or delete what they logged themselves, but everything you logged is read-only to them, and so is the puppy profile, the pedigree ID, your reminders, the exercise list, other guest links and deleting the account. You can still edit anything on your own account, theirs included. The link is shown once when you make it, so copy it then; every live link is listed in Settings with when it expires and when it was last used, and Revoke cuts access off immediately, mid-session. Anything logged on a link is tagged with that link's name in the History log — “💧 Pee · Anna” — and the tag sticks even if you edit the entry afterwards" },