Deprecate + remove the legacy per-tool config once libs/sporeconfig is fully adopted

[scttfrdmn]

Once all four tools adopt the shared libs/sporeconfig base (libs PR #25 + the per-tool adoption PRs), the OLD per-tool config mechanisms should be deprecated and eventually removed, so there's one config system, not two.

What to retire (after the shared base is in + a deprecation window)

• spawn: fold the ad-hoc profile/region resolution into the shared base. SPAWN_INFRA_PROFILE/SPAWN_COMPUTE_PROFILE stay (spawn's two-account split is spawn-specific) but should layer on top of the shared sporeconfig profile rather than duplicate the ambient-chain plumbing. Consider migrating the relevant bits of ~/.spawn/config.yaml (or at least the profile/region story) toward ~/.config/spore/config.toml, keeping ~/.spawn readable during the window.
• truffle: delete the dead .env.example TRUFFLE_* vars (no code reads them) — replace with documented SPORE_*.
• lagotto / spore-host-mcp: remove any bespoke region/profile handling that the shared base now covers.

Sequencing

1. Land libs/sporeconfig (PR spawn launch: should auto-detect minimum volume size from AMI snapshot #25) + per-tool adoption.
2. Mark the superseded env vars / file keys as Deprecated in each repo's CHANGELOG, with the shared replacement.
3. After a release or two (deprecation window), Remove them.

Not to remove

• spawn's infra/compute two-account distinction (deliberate isolation) — it just gains the shared profile as a fallback floor.
• Tool-specific config (spawn DNS/compliance/tables, lagotto tables, truffle timeout) — stays per-tool.

Tracking issue per the shared-config-base work; do NOT action until adoption is complete.