Add studio ui local web surface + converge desktop/local backend (PoC)

[youknowriad]

How AI was used in this PR

Built almost entirely with Claude Code, pairing with @youknowriad. AI authored the studio ui server, the @studio/common extractions, the connector wiring, the auth flows, and the design doc.

Reviewers should start by reading the design doc to understand how everything fits together. They should pay particular attention to:

• The desktop wrappers rewired onto shared modules (cli-site-creator, cli-site-editor, wordpress-rest-api, is-installed, the preview/sync IPC handlers). They are typecheck + unit-test verified and tested quickly.
• Anything touching auth / token handling.

Proposed Changes

Adds a new studio ui surface: the same agentic UI (apps/ui) the desktop shows, served in a browser against the user's real local sites by a small server (apps/local) that is bundled into the CLI and launched with studio ui.

More importantly, it converges the desktop and local backends. Site, session, agent, preview, sync, REST-proxy, app-detection, blueprint, and media logic now live once in @studio/common; the desktop and the local server are thin transports (IPC vs HTTP/SSE) over that same code and the same forked CLI. This stops the two surfaces from drifting and is the main point of the PR.

User-facing (local web):

• studio ui opens the agentic UI in the browser. Create / delete / duplicate / update sites, export & import, open folder/editor/terminal, preview, sync (pull/push), blueprint-based creation, and WordPress.com login (redirect-based) all work against local sites.
• Capability-driven UI: features that need a native runtime degrade gracefully in the browser — editable path field instead of a folder picker, browser downloads instead of Save-As, and the preview's Annotate control is hidden where it can't run.
• No change to the desktop's user-visible behavior is intended; the desktop now runs the shared code paths.

Also adds a design doc, docs/design-docs/studio-apps-and-surfaces.md, mapping the four surfaces (desktop, CLI, local web, hosted), the shared layers, and the convergence.

Testing Instructions

nvm use 24
npm run build:local --workspace=apps/ui   # build the browser UI
npm run cli:build                          # build the CLI (bundles apps/local)
node apps/cli/dist/cli/main.mjs ui         # open studio ui in your browser

[wpmobilebot]

📊 Performance Test Results

Comparing ce8fe3a vs trunk

app-size

Metric	trunk	ce8fe3a	Diff	Change
App Size (Mac)	1311.91 MB	1312.16 MB	+0.25 MB	⚪ 0.0%

site-editor

Metric	trunk	ce8fe3a	Diff	Change
load	1089 ms	1077 ms	12 ms	⚪ 0.0%

site-startup

Metric	trunk	ce8fe3a	Diff	Change
siteCreation	6505 ms	6483 ms	22 ms	⚪ 0.0%
siteStartup	6475 ms	6977 ms	+502 ms	🔴 7.8%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)