warren init --project against a remote server

[jayminwest]

The gap

warren init --project <id> only works when the CLI runs on the same machine as the warren server. Against a remote server it fails with project clone missing on disk, even though the docs present it as the way to scaffold config for a project warren manages.

src/cli/commands/target-dir.ts:44-53 fetches the project row over GET /projects/:id and then checks existsSync(row.localPath) on the machine running the CLI. localPath is a path on the server's filesystem, so on any other machine the check fails and throws. src/cli/commands/init.ts:114-146 then expects to mkdir and writeFile into that path locally. src/cli/commands/config-migrate.ts:80 goes through the same resolveTargetDir and has the same limitation.

There is no write route for this today. src/server/handlers/route-table.ts:192-197 serves only GET /projects/:id/warren-config, and the nearest mutation is POST /projects/:id/refresh (:230-233).

docs/onboarding-external-repos.md:18-39 documents warren init --project as step 2 of the mirror recipe, with no mention that it must run on the host. The comment at target-dir.ts:40-43 records the earlier decision that "writing into the clone only makes sense on the host", which this issue reverses.

What to build

1. A server route that scaffolds .warren/triggers.yaml and .warren/config.yaml into the project's host clone. POST /projects/:id/init with a JSON body carrying the same options the CLI accepts today (default role, prompt, provider, model, branch prefix, and an overwrite flag) is the recommended shape. The handler goes in src/server/handlers/projects.ts next to refreshProjectHandler (:443), which is the precedent for an admin-policy mutation on a project. Reuse the existing template and renderConfigYaml logic from init.ts by moving it into src/projects/ so the handler and the CLI call one implementation (the "single source of truth" rule in AGENTS.md).
2. An SDK method on WarrenClient in src/client/client.ts, beside refreshProject (:174).
3. The CLI switch. warren init --project calls the route. Keep the current local-filesystem path for the no---project case (scaffolding the current directory), which never touches the server. Apply the same change to warren config migrate --project.
4. Docs. Regenerate docs/http-api.md and docs/openapi.yaml (bun run gen:docs, bun run gen:openapi), regenerate the CLI reference if flags change (bun run gen:cli-ref), and drop the host-only assumption from docs/onboarding-external-repos.md.

Scope

Out of scope: committing the scaffolded files upstream (they stay untracked in the host clone, as today), and any change to what the templates contain.

Tests: a new src/server/handlers/projects.init.test.ts following projects.refresh.test.ts; src/cli/commands/init.test.ts gains a remote-mode case (its mockClient at :31 already models projects by localPath, so extend it with the new method); src/cli/commands/config-migrate.test.ts; src/client/client.projects-agents.test.ts. bun run lint includes check-client-contract, which fails if the UI or SDK calls a path ROUTE_TABLE does not serve, so the route and the client must land together.

Getting started

AGENTS.md covers setup, the handler and SDK conventions, and the layer rules (src/cli/** must not import src/server/**). Everything here is testable in-process with no cluster and no credentials. Run bun run check:all before pushing. Warnings count as failures.

Tracked internally as warren-166d.

[jayminwest]

Maintainer note: I am away until Monday, September 14, and will not review or merge PRs before then. PRs for this issue are welcome this week. Comment "taking this" here before you start, and put Closes #1240 in the PR body. @luantaraschi has commit access and can merge a linked PR that passes CI when they have time, but please do not expect a turnaround from them. If this is your first PR to the repo, GitHub holds the CI run until a maintainer approves it, which can take a few days this week. Put questions on this issue, not on the PR. I will work through the queue in the order that the PRs were opened when I am back.