Add aria labels to icon-only controls

[Martinnn674]

Closes #8.

Summary

• Add explicit aria-label values to icon-only controls in the settings modal, rail, channel list, and channel header.
• Keep labels tied to the primary action, e.g. server chips announce opening the server rather than only the mouse-only right-click hint.
• Add a focused source-level regression test for the issue-scoped controls.
• Fix the stale migration test and README sentence that still expected OpenWar to be auto-seeded, matching the current opt-in/default-off behavior described in the changelog and code comments.

Verification

• npx.cmd tsx --test tests/icon-button-labels.test.ts
• npx.cmd eslint components/channel-header.tsx components/rail.tsx components/channel-list.tsx components/settings-modal.tsx tests/icon-button-labels.test.ts tests/migration.test.ts
• npx.cmd tsc --noEmit
• npm.cmd run test:migration
• npm.cmd run test

Notes

• I did not include unrelated package metadata changes from installing dependencies locally.