chore: v0.60.0

[fylorn]

Release for #280 and #281.

• Bump the workspace version to 0.60.0 (Cargo.toml, and the workspace crates in Cargo.lock).
• Add release-notes/0.60.0.md: an opening paragraph, the upgrade notes, and one section each for helper requests and the request history across versions.
• CONTROL_API_VERSION (36) is already at its release value on main; the request store SCHEMA is unchanged (25). This PR does not change them.

Upgrade notes in brief

• Protocol 35 → 36. Lite 2026.10.1 (core 0.59.0) does not connect to 0.60.0; sudo twcore upgrade --version 0.59.0 --restart switches a server back.
• Schema unchanged (25), history kept.
• client_probes takes intercept | forward; a config that still sets passthrough or route does not load. Configs that never set client_probes are unaffected.
• Protocol: ProbeMode is intercept | forward; DryRunOutcome::passthrough and RouteSave.route_probes removed.
• Message codes, from diffing msg-codes.txt and every msg! between v0.59.0 and main: control.unknown_probe_class removed, nothing added, no sentence changed.

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