refactor: split remaining god files and unify the socket command catalog

[arzafran]

One PR for the five open nuclear-review issues. Everything here is file reorganization plus the command-catalog dedup, no behavior change.

What moved

#94 ContentView.swift 7,913 -> 5,791 lines. Window chrome, the window overlay controllers, workspace mount presentation, the vertical tabs sidebar, shortcut hints, internal tab drag, and the sidebar resizer each got their own file (the resizer as a ContentView extension, same shape as the existing command palette extension). TabItemView was already out; it is untouched here.

#97 GhosttyTerminalView.swift 8,446 -> stub. GhosttyApp, TerminalSurface (with the registry and metal layer), GhosttyNSView, GhosttySurfaceScrollView (with its private helper views and the SurfaceSearchOverlay mount), copy-mode types, and shared support each moved to their own file, matching the +Suffix convention the module already used. TerminalWindowPortal.swift 2,079 -> 1,054 with the host view and cross-window registry extracted.

#98 Workspace.swift 5,660 -> 2,056. Sidebar and remote value types moved to model files; the theme, remote glue, surface creation, focus/geometry reconciliation, and sidebar telemetry member groups are now Workspace+X extension files. Sidebar telemetry has one mutation target, as the review asked. The remote-session controller split had already landed on main.

#99 browser trio 13,131 -> 6,139 across the three originals. Browser settings, the whole omnibar subsystem, toolbar views, six BrowserPanel+X concern extensions, and the host/slot/drop views split out. The per-file private helper extensions were kept per-file on purpose so nothing collides; the PageSession facade idea stays future work.

#87 one command catalog. v2Capabilities() now derives from a new V2CommandCatalog and the hand-maintained method array is gone. The 79 copy-pasted invalid-params guards across the TerminalController+* handlers collapsed onto one v2InvalidParam() helper. On the CLI side every per-command usage text moved into the CommandDescriptor table and the ~1,300-line subcommandUsage switch is deleted. The dispatch switch itself is untouched, as the review cleared it. The per-family usage helpers that already live next to their descriptors in CLI/CLI+*.swift were left alone.

Guardrails and verification

• Typing-latency paths moved byte-for-byte: WindowTerminalHostView.hitTest() and TerminalSurface.forceRefresh() diff clean against main; key handling untouched.
• App, CLI, and unit-test targets all build locally.
• CLI top-level help and 27 sampled per-command --help outputs are byte-identical to the shipped release binary; help <cmd> rejects arguments exactly like before.
• Capabilities JSON was already sorted before serialization, and the catalog carries the same method set including the DEBUG-only block.
• Access-level flips (private/fileprivate -> internal) were made only where a file boundary now sits between a member and its callers; each agent's report lists them.

Closes #87
Closes #94
Closes #97
Closes #98
Closes #99
Closes #104