feat(gui): configure Easy-Switch followers

[noobydp]

Fork staging PR: The upstream draft is AprilNEA#1123. This is
stacked on the reliability review in #2, so the fork PR shows only the single
GUI and capability commit.

Summary

Add a capability-gated Easy-Switch panel for keyboards with reportable host
controls. Users can select locally known ChangeHost-capable followers without
editing TOML, using the existing physical device identities and
host_switch_targets configuration.

Changes

• openlogi-core - append measured host_switching and
  host_switch_controls flags to device capabilities while keeping old cached
  inventories compatible.
• openlogi-device - probe 0x1814 ChangeHost and the reportable 0x1b04
  host-control table through one named capability plan.
• openlogi-ipc / openlogi-agent - carry the two appended capability flags
  in inventory protocol v30 and update the mock inventory. Follower settings
  do not gain a new IPC mutation.
• openlogi-desktop / openlogi-ui - render the follower selector, persist
  the pre-existing host_switch_targets field directly, request the existing
  agent config reload only after a successful save, repaint failed rollbacks,
  reject self-links, and provide locale-complete copy.

Screenshot

Pending the final GUI smoke test. Keep this PR in draft until a screenshot is
attached.

Testing

• cargo fmt --all -- --check
• RUSTFLAGS="-D warnings" cargo clippy --workspace --all-targets -- -D warnings
• RUSTFLAGS="-D warnings" cargo test --workspace
• cargo test -p openlogi-ipc --test wire_format
• cargo test -p openlogi-desktop i18n
• RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps --document-private-items --exclude openlogi-ui --exclude openlogi-desktop --exclude openlogi-overlay --exclude openlogi-agent
• RUSTFLAGS="-D warnings" cargo check -p openlogi-hidpp -p openlogi-device --target wasm32-unknown-unknown
• typos was not run locally because typos-cli is unavailable.
• Not manually smoke-tested at this final head. Before marking ready, select
  and clear a follower, restart the app, confirm the selection persists, and
  attach a screenshot of the Easy-Switch tab.

Depends on #2 and AprilNEA#970

Code and PR drafted with Codex