feat(server): run a repository's t3.json setup action automatically

[tusharbhardwaj-bk]

Problem

A repository could already declare scripts[].runOnWorktreeCreate in its checked-in t3.json, but the server only read that file for the project icon. The scripts were surfaced solely as a manual "Add action" import in the web UI (ProjectScriptsControl.tsx → importFileScript), so a repo that commits its setup action still came up with nothing running until a human clicked through it — once per project, per T3 instance. The motivating case is bk-docs, whose committed setup script symlinks gitignored .env files into each new worktree: without the import, every new worktree started with no .env.

Fix

ProjectSetupScriptRunner now falls back to t3.json when a project has no persisted worktree-setup script. It takes the first entry flagged runOnWorktreeCreate and synthesizes a ProjectScript under the stable id t3-json-setup (which only names the default setup terminal and appears in bootstrap receipts — the Coordinator always passes preferredTerminalId).

• A persisted project script always wins; the checked-in file is only the fallback.
• T3ProjectFileLoader.load is infallible, so a missing, unreadable, or malformed t3.json still means no-script, never a bootstrap failure — and no new error channel.
• The T3ProjectFileScript → ProjectScript conversion lives next to setupProjectScript in packages/shared/src/projectScripts.ts, mirroring the web import path's defaults (icon ?? "play").
• server.ts provides T3ProjectFileLoader.layer to the runner inside GitManagerLayerLive; FileSystem/Path already come from PlatformServicesLive.

Every fork edit to an upstream-owned file sits inside a T3-CUSTOM(expbkt3) marker.

Verification

• vp test run src/project/ProjectSetupScriptRunner.test.ts — 9 passed, including new coverage for: persisted script wins over t3.json; t3.json used when there is no persisted script; no t3.json; no qualifying t3.json entry; malformed t3.json → no-script.
• tsgo --noEmit clean in apps/server and packages/shared; targeted vp lint and vp fmt --check clean.
• Repo-wide suites deliberately left to CI (shared dev box).

Retargeted to expbkmain per the fork's ship-to-staging rule in AGENTS.md; origin/expbkmain is merged in, so CI validates against the real base.

Note: the markers CI job is already failing on both fork branches (see PR #55) from a pre-existing baseline backlog unrelated to this change; none of the files touched here are flagged.

Docs: docs/user/worktree-setup.md gains a "Ship the setup action in the repository" section.

Model: Claude Opus 5. Harness: Claude Code in T3 Code.

🤖 Generated with Claude Code

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