[EhabY]

External app links now follow the same $SESSION_TOKEN rules as the dashboard (coder/coder#31208).

• The token is filled in only when the link opens a known Coder IDE handler, its url param is the sign-in URL or the deployment's dashboard_url from build info, and the placeholder is the token value.
• Dev container (sub-agent) apps have the placeholder removed before anything else, as coderd does since fix!: validate workspace app URLs on the server coder#31262.
• Links that need a token but don't match are shown disabled. The tooltip names both URLs when the link points to another deployment, and otherwise uses the dashboard's message.
• Links that don't open a known Coder IDE handler ask for confirmation before opening, like the RDP prompt. "Don't ask again for scheme: links" saves the scheme in UserDefaults.
• The VS Code links percent-encode the host and directory.
• SDK: read parent_id from the workspace agent and dashboard_url from build info.

Decision log

• Same rules as the dashboard: all clients agree on which links get a token.
• dashboard_url kept in memory, not saved: an admin can change the access URL, so it's fetched again on each launch and sign-in.
• Strip the placeholder for dev container apps: there's no token to protect, so old and new servers behave the same and the token can't reach those links.
• Disabled icon instead of hiding the app: the tooltip says why it can't open and who can fix it.
• NSAlert for the confirmation: same as the RDP prompt and InvalidAgents, since .alert doesn't work well from the menu bar.
• Confirm only links outside the known handlers: IDE links stay one click.
• Remember per scheme: like a browser's external protocol prompt. Uses the same checkbox and UserDefaults pattern as the hidden menu bar icon alert.
• ASCII only, split on scalars: URL(string:) percent-encodes non-ASCII, and Swift compares strings by grapheme, so & or = followed by a combining mark would otherwise not split.

Same commits as #275, which merged into fix/xcode-27. That branch was later rewritten and no longer contains them. They sit directly on main, so this PR is #275's diff against main.

Tests: the menu UI and the confirmation alert weren't run by hand.

Generated with Coder Agents.