fix: 30 day sliding session TTL instead of a hard 24h expiry

[ConalMullan]

Problem

OAuth sessions expired after 24h, so every hosted user had to complete a full browser sign-in daily.

The interesting part is why. Decoding the DS access token from a live dev session:

DS access token issued : 2026-08-12
DS access token expires: 2027-08-12   (life: 365 days)
our session expires    : 2026-08-13   (life: 24 hours)
BINDING CONSTRAINT     : our 24h session TTL

The DS token is good for a year. Our own TTL was forcing re-authentication — and since we issue no refresh_token and advertise only the authorization_code grant, a client has no way to renew without user interaction.

This also corrects the earlier plan to implement token refresh: refresh solves an expiry we don't actually have.

Change

• TTL.SESSION: 24h → 30 days
• Slid forward on each authenticated request (touchSession), so an actively used connection never expires. 30 days becomes an inactivity window rather than a hard cap.

Kept well inside the DS token's 365-day life because a session ID is a bearer credential.

Two implementation details:

• The slide only writes when the expiry has moved by more than an hour, so a busy session touches the store roughly hourly rather than on every request.
• It is fire-and-forget — a failed extension logs a warning and never fails the request the user actually made.

Verification

Built server reports TTL.SESSION = 2592000s (30 days), which is also the expires_in we advertise to clients.

New tests cover both directions:

• an active session survives 50 days of use (5× the old TTL, past a static 30-day one)
• an unused session still expires
• touchSession will not resurrect an already-expired session
• it skips the write when the expiry has barely moved, and reports whether it extended

The existing exposes TTLs in seconds test is updated, plus a new intent-based assertion (> 7 days, < 365 days) so the reasoning is pinned, not just the constant.

553 tests passing (was 547). Lint and format clean.