[Kheartz]

Adds a Gates guide to the World section, brings the Doors guide up to date, and links the two.

The Gates guide covers:

• that gates are not doors: no Doors call reaches a gate, and no Gates call reaches a door;
• the four kinds and what each supports: portcullis (opens, closes, locks), runeGate (opens past its puzzle, closes), swingGate (opens, closes) and crawlGrate (opens one way, by breaking);
• client Gates.list and its row fields, setOpen, setLocked, freezeSchedule, setPolicy, policy() and held();
• server Gates.set / get / list / clear / clearAll, and how held state combines with the policy;
• the doors resource's gates: rules (kind, open, lock), heldGates, gateSchedule and the gate commands;
• gotchas: the Clocktower gate's three actors, scoping wide opens with kind, freezing portcullis schedules, and gates a player opens their own way not being shared.

The Doors guide gains:

• a pointer to Gates;
• a section on shared unlocks: Doors.setShareUnlocks / getShareUnlocks and the doorUnlocked event;
• doorUnlockRequest details: at most once a second per door, the other leaf of a double door, and an empty selector for a lock the player's own policy keeps shut;
• holding both leaves of a double door;
• "key-only locks included" for the master key (superAlohomora);
• a section on the doors resource: the held config, /listdoors, /doorset and /doorsheld;
• a fix: unlocking with Doors.set unlocks the door for everyone. It does not open it.

The overview lists the new guide under World.

Depends on a contract republish. The Gates API landed on mod main in 718af20e, but the published testing contract is still 1.9.2, which has no Gates. Until a contract from that commit or later is published, docs:check fails on the five Gates samples:

guides/World/gates.md:31:22 - TS2304 (client): Cannot find name 'Gates'.
guides/World/gates.md:61:1 - TS2304 (server): Cannot find name 'Gates'.
guides/World/gates.md:62:1 - TS2304 (server): Cannot find name 'Gates'.
guides/World/gates.md:86:16 - TS2304 (client): Cannot find name 'Gates'.
guides/World/gates.md:102:1 - TS2304 (client): Cannot find name 'Gates'.

The guides don't link into the API reference, so nothing here breaks while the reference lacks the Gates types.

Tested locally:

• docs:check: all 183 samples type-check against a contract built from mod main 718af20e;
• pnpm build and docs:links: every link and anchor on 50 pages resolves;
• checked the built Gates and Doors pages: Gates sits between Doors and Loot in the sidebar, and every table and code block renders.