Fix: framed pages could not read vault content · Dev renamed to Internal

• The library, the talks and the deck failed to load. Root cause: a page running inside the host's srcdoc stage frame usually cannot reach the SG bridge, and its relative fetch() resolves against the parent's base rather than the vault root — so both routes to vault content failed, and the page showed "The library could not be loaded." Reproduced exactly before fixing.
• The fix is to ask the host. The host is the context that loaded the page in the first place, so it demonstrably has a working reader. It now answers a read RPC over postMessage (rm-read → rm-read-result, text or binary), and framed pages go through RM.services.vaultIo, which tries the direct bridge first, then the host, then plain fetch for the standalone case. This was the missing piece in the 0.5.4 externalisation: content stopped being inlined, but the frame was never given a reliable way to fetch it back.
• A smoke group now reproduces the exact failure conditions — no bridge reachable, fetch returning 404 — and asserts the articles, talks and deck all still load.
• "Dev" is now "Internal" in the navigation, since "Dev" reads as developer documentation rather than the internal release log. The file stays dev.html: frozen versions link to it and, by design, cannot be edited.