Redesign tb resources: two-line view (secure environment + per-run allocation)

[LukasWodka]

Part of epic tracebloc/backend#1142 / cli#355. Implemented by PR #359.

Bare tb resources shows the allocation in two lines + a pointer to the scriptable set — no inline prompt, no physical-host line:

 Your secure environment is equipped with: 8 CPU · 32 GiB
 A training run is allocated up to: 4 CPU · 16 GiB
 Do you want to change the allocation? Run `tb resources set` (guided on a terminal).

• Line 1 — secure environment total: what the cluster can schedule.
• Line 2 — per-run ceiling: the per-training allocation (cluster-wide, uniform — the only CLI-settable dial).
• Change it: tb resources set (flags for scripting; guided walkthrough on a TTY). Bare resources never mutates.
• --verbose: per-node breakdown + raw values.

History / scope change (2026-07-21)

Originally scoped as a 3-layer view (machine / secure environment / per-run) plus an inline guided-change wizard. Per Lukas's "just two lines" direction this was simplified to the two-line view above. Dropped:

• the "Your machine has:" physical-host line (the "this machine" vs "tracebloc uses" framing confused users), and
• the inline [y/N] prompt (replaced by a plain pointer to tb resources set).

The full 3-layer spec and its implementation live in the closed PR #361 if we ever revisit the richer view.

[LukasWodka]

Implemented by #359 (merged) — the two-line resources view. (Retitled earlier to match what shipped.)