feat(cli): deck edit — change a deck without deleting it

[jvsena42]

Closes #222.

loopky could create a deck and edit every card in it, but nothing about the deck. The only workaround was deck delete + deck create --from-file, which mints a new deck id — every pubky://…/decks/<id>/ link breaks, every card goes back to new in the scheduler — and which is impossible for a deck built with card add, since there is no file to recreate it from.

deck edit <deckId> [--title T] [--description D] [--cover-url URL] [--cover-emoji E]
                   [--tag T]... [--clear-tags] [--clear-cover]
                   [--listen|--no-listen] [--speak|--no-speak]
                   [--type|--no-type] [--reverse|--no-reverse]
                   [--front-lang BCP47] [--back-lang BCP47]

One updateMetadata call — the manifest and the tag records, never the chunks — so it costs the same on a 20k-card deck as on an empty one.

The rules, and why each one is the surface's own

• An absent flag leaves its field alone, card edit's rule; an explicitly empty value clears it (--description=, which is --back=). --clear-tags / --clear-cover are switches because those two are not single values: --tag "" would have to mean both "no tags" and "one blank tag", and a cover is an emoji and an image that layer.
• --tag replaces rather than appends, as the issue proposed. Appending makes "the tags are exactly these" unsayable without a delete, and makes a retry after the hourly session expiry (Every homeserver write dies on /session with a raw transport error, and publish reports it as "check your connection" #165) grow its own list — the same property card add's dedupe exists for.
• Nothing to change is not a write. A manifest write bumps updated_at, which is what every follower's "the author published changes" badge reads, so a re-run reports changed: false and leaves the record alone.
• The derived language labels are reconciled only when the pair actually moves. Retyping a deck from Spanish to French drops spanish; --clear-tags on a language deck stays empty, because those are ordinary author-removable tags rather than a reserved family (Architecture §7.7).

--json gets {deck, changed, fields} — fields names what actually moved, diffed against the stored deck rather than read off which flags were typed, so it is something a caller can verify against.

Two answers to the issue's open questions

The study-mode toggles are in, not split out. Turning one off costs no progress: review state is keyed by card_id alone and the modes decide only how a card is presented. Reverse's pairing is session-local and persisted nowhere, so even that one has nothing to lose.

--cover-url and --cover-emoji are not mutually exclusive, and they are not exclusive in deck create either. They are separate manifest fields, and DeckTile draws the image over the emoji — the emoji is the fallback when the image fails to load. Refusing the pair would have broken that. Both are settable in one call; --clear-cover removes both halves.

One thing this deliberately does not fix: deck create --front-lang es-ES still writes no spanish/language label, because it never did. That is a separate gap and changing an existing command's behaviour did not belong here.

Verification

./gradlew detektAll :cli:test green; 15 new tests in DeckEditTest covering the overlay, the two clear gestures, tag replacement, the retag, the no-op write and every refusal.

Then driven against a real staging homeserver on the live session, on a throwaway deck created and deleted in the same run, with two cards added partway through. Full table in journeys/RESULTS.md; the load-bearing rows:

Step	Result
The same edit twice	changed: false, updated_at unmoved — no second write
Edit a deck with 2 cards	same deck id, card_count: 2, chunk table unchanged, card list intact
deck show in a fresh process	every change is on the homeserver, not just in the cache
--back-lang fr-FR	spanish dropped, french added, the author's own tags kept
--clear-tags on a language deck	[] — the derived labels are not put back
--cover-url http://…	exit 9, refused before the write
--clear-tags --tag x, --title=, --clear-cover --cover-emoji	exit 2 each, refused rather than guessed at

🤖 Generated with Claude Code

https://claude.ai/code/session_0116NZ92Pe7aGQpqtiRkP4Ye