Standby: small inconsistencies

[raethlo]

Let 🤖 run through the docs to map out incomplete standby docs.

Actual contradictions:

• running/actor_standby.md:91 — claims Standby isn't configurable at Actor level; the dev page (:20) says the Settings tab works.
• programming_interface/actor_standby.md:208 — says users cover platform costs in PPE; pay_per_event.mdx:68-70,95 says it's opt-in.
• Same file :104 — uses standbyPort/standby_port, but :44,62 use containerPort/web_server_port.
• running/actor_standby.md:103 — absolute "runs not shared with other users". Becomes false the moment multitenant ships.
• running/actor_standby.md:59 — stale "Standby Beta"; "beta" appears nowhere else in the Standby docs.

Missing:

• web_server_schema/index.md:93 — never says the schema is validated at build time only, not against requests/responses.
• running/actor_standby.md:18 — page never mentions MCP or webServerMcpPath, even though the Standby URL is the MCP endpoint.
• web_server_schema/index.md:108 — related-fields table omits webServerMcpPath.
• programming_interface/actor_standby.md:20 — usesStandbyMode never mentioned on either Standby page.
• running/actor_standby.md:96 — "Billed differently" omits who pays for monetized Standby compute; and the Standby PPE exception is missing from the canonical pay_per_event.mdx:93.
• running/actor_standby.md:75 — omits the 2-minute run-selection timeout (documented only on the dev page, :180).