panel-redesign: the application form is one POST, under its domain

Stage 1, step 4 (plan § Routes).

Service (internal/app)
  - Settings{Mode, Addresses, AuthIPRestrict, AuthAllowedIPs, Limit} is what
    the form holds besides the login. CreateWithSettings creates the
    application with all of it and removes it again if a later write fails;
    SaveSettings validates the sender rule first and, if a later write
    fails, puts back what it had already changed. The form produces a whole
    application or leaves things as they were.
  - Limit.Mode "" is "use the domain limit"; auto takes its ceiling from a
    recalculation the caller supplies.

Routes and handlers
  - GET, POST /outbound/domains/{id}/applications/new
    GET, POST /outbound/domains/{id}/applications/{aid}
    POST .../{aid}/password, .../{aid}/ratelimit/recalc, .../{aid}/delete
    replace POST /domains/{id}/applications and the six /applications/{aid}/*
    routes. lookupDomainApplication answers 404 when the application is not
    in the domain named by the path - also when the caller may open that
    domain.
  - A generated password is the response to its POST only (no GET path) and
    is sent with Cache-Control: no-store.
  - The login is not renamed by the form; a changed login is a 400.

Old domain page: the three per-application forms (mode, IP restriction,
limit) are one form with one Save; "Remove limit" became the "Use the domain
limit" choice. The e2e client follows (edited, not run here).

Tests: service - create and save in every limit mode, and all-or-nothing on
a refused sender rule, a failed recalculation and a failed sender-map
rebuild; handlers - the form's parsing, one POST creating sender + IPs +
limit, four kinds of refused form creating nothing, save, the no-store
header on both password pages, and five application routes against another
tenant's application addressed through its own domain and through the
caller's.

With @routes removed by hand TestRoutesFollowNavigation now reports only
GET /server/health (step 5).

go test ./...  green except the two Windows-only failures in internal/domain
and internal/logtail.

Roadmap 14/27.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plans/panel-redesign.md

@@ -508,7 +508,7 @@ only when both are done. Every stage-2 step ends with the evidence of
 - [x] Schema from zero: single `0001_init.sql` baseline with `users.email`, the DMARC default fields, `user_inbound_domains`, the two `all_*` flags; store tests; `schema-migrations.md` rewritten — **Opus**
 - [x] Inbound delegation: `requireInboundDomain`, lists and log filtered in the query, two-list user form data, per-route 404 tests for both roles including another tenant's id — **Opus**
 - [x] Routes renamed per § Routes: new paths, one fragment name, old paths removed, subtree `requireGlobal()` for `/server/`; links in the old templates retargeted so the panel works on every commit — **Opus**
-- [ ] The application form as one POST; `out-app-created` as the response with `Cache-Control: no-store` — **Opus**
+- [x] The application form as one POST; `out-app-created` as the response with `Cache-Control: no-store` — **Opus**
 - [ ] Server › Health route and handler (tables and *Reload configuration* from `/status`); Overview handler reduced to verdicts — **Opus**
 
 **Stage 2 — pages, in groups** (each step: partial calls only, page off the ratchet list, evidence pairs)