feat(routing): cross-repo task routing + orphan-branch cleanup (#17)

Two related fixes for the agent-workflow defects exposed by the
2-May-2026 batch:

1. **Cross-repo task routing** (`task.repo_url` override).
   `resolveRepoRoot` now consults `task.repo_url` first; matches against
   per-repo env-var (`SCRUM4ME_REPO_ROOT_REPO_<name>`),
   `~/.scrum4me-agent-config.json` `repoRoots[<name>]`, and finally
   `~/Projects/<name>/.git`. Falls back to product-level resolution
   when null. Tasks tracked under one product but targeting another
   repo (e.g. MCP-server tasks under the main product's PBI) now work.
   `getFullJobContext` exposes `task.repo_url` to the agent.
   `attachWorktreeToJob` accepts and forwards it.

2. **Orphan-branch cleanup** in `createWorktreeForJob`.
   Previously a name-collision suffixed with a timestamp, leaving the
   agent on an unpredictable `feat/story-XXX-<ms>`-name. Worse, in the
   2-May batch the agent ended up reusing an orphan branch from an
   earlier story (`feat/story-x35n155c`) and pushed to a remote ref
   that did not exist, causing 'src refspec does not match any'.

   Now: detect orphan, attempt to remove its (stale) worktree if any,
   delete the local branch, and recreate with the predictable name.
   Timestamp-suffix is the last resort.

Vendor submodule bumped to pick up `Task.repo_url` from Scrum4Me #54.

Tests: 129/129 — `suffixes branch name with timestamp` updated to
`removes orphan branch and reuses the predictable name`.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vendor/scrum4me

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-Subproject commit e02c6ff9d9eef142cd72011d46f565a10e4b23ac
+Subproject commit a754acf13ba68c411d73060537ef356037230065