fix(core): reset steps for promoted prompts

[kitlangton]

Summary

• reset the configured agent step allowance whenever newly admitted user input is promoted, including steering prompts
• describe queue behavior in terms of continuation and process-local Session drains instead of an invented Activity domain concept
• remove stale 25-turn-cap documentation and tests, then regenerate the SDK/OpenAPI descriptions

Testing

• bun run typecheck in packages/core
• bun run typecheck in packages/server
• bun run test test/session-runner.test.ts in packages/core (80 passed)
• git diff --check

Review note

The requested parallel simplify agents could not start because their local session database is missing the replacement_seq column. The focused test and typecheck verification above passed.