fix: secret ordering, dead-end opens, and stale response metrics

[starvy]

Three fixes that came out of a hands-on UI audit, each verified end-to-end in the running app on Linux (real sends against api.github.com and a local streaming server).

1. Secrets resolve only after the host allow-list decision — fix(engine)

Sending to an off-list host with inherited {{secret:…}} auth used to resolve the secret first: an unreachable keychain failed the whole send over a credential the policy would never let it carry, and every refused send cost a secret-backend read. The egress decision now comes first — refused destinations skip resolution entirely and go straight to the policy dialog; Send once / Allow host re-enter with the grant and only then resolve. The Auth-tab mismatch warning now uses the same policy::egress_allowed predicate as the send path, so the two can't drift.

New engine tests prove the ordering with a counting resolver double: off-list host → zero backend calls, no Authorization header, one strippable OffHostEgress; granted host → exactly one read, and a broken backend still errors as before.

2. Failed workspace opens no longer dead-end — fix(ui)

• A recent whose folder is gone is marked missing in the Welcome list; opening it prunes it from the persisted recents and the toast says so. Only NotFound + path-actually-gone prunes — permission errors and malformed manifests keep the entry.
• A path picker that can't open at all (Linux without xdg-desktop-portal) used to be a silent no-op; New/Open Workspace now toast the underlying cause.

3. History rows carry their numbers; elapsed ticks live — feat(ui)

• History rows now show the recorded latency and size (200 · 10.21 s · 170 B) next to the age.
• The in-flight elapsed only rendered before the first byte, so it read as a frozen counter that jumped to the final total. It now counts through the whole flight (1.9 s · 32 B received → 5.0 s · 89 B received), quantized so the low digits don't strobe at repaint rate; the settled total remains the engine-reported elapsed.

Gates

cargo test --workspace (413 passed) · cargo clippy --workspace --all-targets -- --deny warnings · cargo fmt --all --check

Review notes

• History-row metadata is flex_shrink_0, so long ad-hoc URL names truncate hard in a narrow sidebar (saved-request names are fine). Shout if you'd rather the metadata yield instead.
• The same picker-failure swallow still exists in the OpenAPI-import and multipart file pickers (interchange.rs, multipart.rs); the new picked_folder helper is liftable — left as a follow-up to keep this reviewable.
• Screenshots live on the throwaway assets/ui-audit-fixes branch; delete it whenever this PR is closed out.