feat(cua-driver)!: remove browser approval tokens

[f-trycua]

What changed

• authorize driver-owned isolated browser preparation through the runtime permission mode and optional capability manifest
• keep existing-profile attachment behind launch grants, bounded manifests, authorization hosts, or unrestricted startup acknowledgement
• remove browser-approve, approval_token, the legacy launch flag, temporary approval artifacts, and MCP prepare markers
• update CLI fixtures, Rust tests, public docs, and bundled browser guidance

Why

The file-backed token was a second authorization system that predated runtime-owned permission profiles, manifests, grants, and authorization hosts. Removing it gives every transport the same runtime authorization contract.

Impact

This intentionally removes a public CLI subcommand and MCP input field. Direct isolated-browser callers no longer need to mint or forward a token. Existing-profile callers must use one of the supported runtime authorization paths.

Validation

Final head: 25a96734781086539a5d327e718048d8b82ab597

• cargo fmt --all -- --check
• cargo test -p cua-driver-core -p cua-driver -p cua-driver-sdk -p cua-driver-testkit
• cargo test -p cua-driver --all-targets --no-run --locked
• generated documentation sync and link checks
• canonical Linux interactive E2E: run 31885879462 at executable candidate 6221b2823903ce323577037bb9dda7adfd5e1101 — passed
• canonical Windows interactive E2E: run 31885880756 at executable candidate 6221b2823903ce323577037bb9dda7adfd5e1101 — passed
• standalone browser E2E (Windows Chrome/Edge and Linux Chrome): run 31885881911 at executable candidate 6221b2823903ce323577037bb9dda7adfd5e1101 — passed
• canonical macOS interactive E2E at 25a96734781086539a5d327e718048d8b82ab597: native 157/157 and installed-browser 18/18, zero failures — passed

The only commit after the Linux/Windows E2E candidate regenerates mcp-tools.mdx; it does not change executable behavior. macOS ran the final head. A full rerun confirmed an earlier AppKit timing failure was transient.

Closes #3184

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