feat(vscode): Stream Deck controller support (follow-focus + relay verbs)

[amrmelsayed]

What

The extension-side changes that let the Codev Stream Deck plugin work. The command-relay substrate landed earlier (#1091); this PR is the consumer half that lives in the VS Code extension. The plugin package itself lands separately.

~178 lines, 5 files, all in packages/vscode. No core/types/Tower changes, no new dependencies, no lockfile churn.

Why it's safe to land on its own

Every bit is inert without a Stream Deck:

• the follow-focus code is gated behind codev.streamdeck.followFocus (default off), so it never fires a streamdeck:// URL unless you opt in;
• the relay verbs only run when a controller sends them over the existing command relay.

Non-Stream-Deck users see zero behavior change.

Changes

File	What
src/streamdeck-focus-sync.ts (new)	Passive deep link (streamdeck=hidden, never foregrounds the app) announcing the focused workspace and the active builder; gives up + warns once if there's no handler.
src/extension.ts	Hooks (into existing subscriptions): announce on window focus, and the active builder from a focused diff / terminal / sidebar row; plus the codev.focusWorkspaceWindow command (vscode.openFolder(uri,{forceNewWindow:true}) to focus a workspace's existing window — fork-agnostic).
src/terminal-manager.ts	getActiveBuilderId() — maps the focused builder terminal to its builder id.
src/command-relay.ts	Allowlist: focus-workspace -> codev.focusWorkspaceWindow, scroll -> editorScroll.
package.json	The codev.streamdeck.followFocus setting (default false).

Feature groups

1. Workspace follow-focus — the controller follows the focused VS Code window.
2. Controller -> VS Code window focus — selecting a workspace on the controller reveals its existing window.
3. Scroll dial — the scroll verb maps to the built-in editorScroll.
4. Builder follow — the controller follows the active builder (diff / terminal / sidebar), keyed on the builder id.

Verification

• check-types + lint pass (identical files were verified on the source branch; main is undiverged in packages/vscode).
• Behavior verified on hardware (Stream Deck +): workspace + builder follow both directions, opt-in gating, no focus-stealing (passive deep link).