fleet: busbar pin -> predev 1d111f2904; pack at the plugin's own version

[MattJackson]

Pin. busbar 7356bbfb6baeb0e9245a59dc74f8b4bfadb2c5a4 -> predev tip 1d111f29049842e66f4ce3419e1219302a249b4f (1.6.0). The pin moves in .busbar-ref, the workflow revs (ci, release and its consumer-verify call, repin), the workspace's busbar git deps and [patch], the fleet dependency table and the deny.toml header. busbar-transport-http moves to a715d1ab57 and busbar-transport-tcp to eb334dd6e9, the revs busbar links at the tip. Cargo.lock moves busbar's crates to the tip and resolves with cargo metadata --locked.

Adaptations.

• The template files are the busbar-release render (template 4c47cad0385d) that fleet: the busbar-release plugin template (CI, deps policy, settings) #21 carries at 276a156148, retargeted to the tip. busbar-contract, plugin-loader, core-connector, the root workspace table, .github/fleet/deps.toml and busbar's Cargo.lock are identical between 276a156148 and the tip, so only the rev moves. The hunks overlap fleet: the busbar-release plugin template (CI, deps policy, settings) #21 only where the rev moves. They are disjoint from export-webhook: a userinfo in the URL is sent as authorization: Basic, as 1.5.5 sent it (audit export-webhook #1, HIGH) #19, which touches lib.rs and an earlier region of tests.rs.
• export-webhook/src/tests.rs: the contract's HostTables gained the appended io table (abi/host/io.rs, the host's io.*). The ready test's host tables lend none (io: std::ptr::null()). This was the one compile error in fleet: the busbar-release plugin template (CI, deps policy, settings) #21's CI (E0063).
• Export kind and SDK: nothing else this plugin uses changed shape. abi::export (ABI 3) and mechanism::{call,door,ticket::Ticket} are unchanged, and so are sdk::{door,exchange}, plugin_door! and export_door!. connector::{Need, DIRECTION_OUTBOUND, EGRESS_OPEN_WEB, KEEP_NAMED} changed only in comments (the RANDOM slot is retired). Life, Held, Lent, Out, Safe and SafeSlot gained only crate-private items; Held::release went pub(crate) and is not called here. conn::DeclaredConns::hold_authority has a default.
• Conformance harness: the conformance_suite! surface (door, cdylib, inputs, host, tls) is unchanged. The export script now lends each batch through the dispatcher and reads only answers the host judged. far_ends is an optional input. The new RED arms come in through the macro, and conformance.json needs no change. declares.json's contract_abi 3..3 still matches the export ABI.

Pack-version fix (ARCHITECT ruling C'). busbar-plugin-pack --version must equal the plugin's own Statement version. predev has no binary-version first-party floor: first-party plugins version on independent lines (plugin-loader sign.rs:28-30). This repo has no test that packs at busbar --version: there is no busbar_version helper, no admin_api_e2e.rs and no e2e.rs. The conformance suite opens the built cdylib, and the Statement carries env!("CARGO_PKG_VERSION"). So the ruling needs no hunk here. Note: the crates are versioned 1.5.0, while plugins.yaml gives this repo version_line: "1.0".

Layout proof. This is a Rust plugin. It vendors no abi-layout.golden or busbar_plugin.h and has no layout assertion test. The contract it compiles against is busbar-contract at the pin, so with the pin equal to predev's tip its compiled-in ABI layout is predev's by construction.