fix(cli): vault names join with "--", not "/" — the server rejects slashes (#112)

#109 addressed vaults as <project>/<env> and shipped broken: every push
failed with

    Vault name must be lowercase letters, numbers, and dashes.

The vault-create endpoint slugifies through /^[a-z0-9][a-z0-9-]{0,62}$/
(apps/pwa/src/routes/credshare.mjs), so a "/" join is refused outright.
Nothing in the CLI ever saw it, because the tests exercised vaultName and
splitVaultName in isolation and never made a request — the one assumption
that mattered, that the server takes an arbitrary vault name, was the one
left unverified.

Switches the separator to "--", which is inside the allowed character set
and still splits unambiguously since neither half may contain one. A
single dash would not: "a-b" + "c" and "a" + "b-c" would collide.

Also validates the joined name against the server's own regex before the
request, so a bad name fails locally with a useful message rather than a
422 after the .env has been read.

The tests now assert the produced name matches that regex, so the
separator cannot drift back out of the allowed set without failing.

Verified end to end against app.logicsrc.com: push, then pull into a
scratch file and diff — keys and values both round-trip losslessly. Then
49 repos pushed under the profullstack team; server reports 49 vaults,
169 secrets, 0 failures.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/credential-sharing.md

@@ -183,7 +183,9 @@ re-wraps (seals) it to the new member's public key. The private key lives only i
 logicsrc login
 
 # Owner: create a team, push a local .env into an encrypted vault, invite people.
-# A vault is addressed as <project> <env>, stored as the vault name project/env.
+# A vault is addressed as <project> <env>, stored as the vault name
+# project--env (a double dash: the server slugs vault names through
+# /^[a-z0-9][a-z0-9-]{0,62}$/, so a "/" would be rejected).
 logicsrc teams create acme --name "Acme Inc"
 logicsrc teams push acme web prod --env .env    # encrypt + upload
 logicsrc teams invite acme teammate@example.com # emails an accept link