feat(ci): reuse lane across PR commits + adopt-on-conflict for concurrent runs

[davidfirst]

`bit ci pr` now reuses the existing remote lane on subsequent commits to the same PR rather than deleting and recreating it. This preserves lane history, lane-based cloud UI edits, and prevents archived-lane pileup. When two CI runners race the first push, the loser adopts the winner's lane and rebases its snapped Version parents onto the remote heads — preserving both runners' snaps chained on the lane and avoiding a costly re-snap with `--build`.

Changes

• snapPrCommit (`scopes/git/ci/ci.main.runtime.ts`): switch to existing lane if remote has it, then merge main into the lane to bring forward config-only changes (deps/env set) that aren't git-tracked. Otherwise create fresh fork from main.
• adopt-on-conflict: catch the "different hash" error during export, fetch the remote lane, rewrite snapped Versions' parents to point at the remote heads (in-place — Bit Versions aren't content-addressed), swap the local lane for the remote one, re-export.
• scope-index LaneId uniqueness: new `validateLaneIdUniqueness` check, invoked before `writeObjectsToTheFS` writes files — surfaces the concurrent-push conflict early and leaves no stale objects on the remote.
• export persist cleanup: `pushToRemotesCarefully` now removes pending dirs when persist fails, so a retry isn't blocked behind a dead client in the queue.

Test plan

• `bit ci pr workflow` — baseline still passes.
• `bit ci pr reuses the existing remote lane across subsequent PR commits` — sequential commits stay on one lane.
• `bit ci pr merges main into the lane on subsequent runs (config-change propagation)` — `bit deps set` on main flows onto the lane via `bit lane merge main`.
• `bit ci pr with concurrent runners on the same PR branch` — two cloned workspaces race; loser detects conflict, rebases, retries; both snaps end up chained on a single lane.
• All 48 ci-commands e2e tests pass.
• Lint clean.

[Copilot]

Pull request overview

This PR updates the bit ci pr flow to preserve and reuse a PR’s remote lane across subsequent commits, and adds a conflict-recovery path for concurrent CI exports so racing runners can converge on a single remote lane without forcing a costly re-snap/build.

Changes:

• Reuse existing remote PR lanes (instead of delete/recreate) and merge main into the PR lane to propagate non-git-tracked config changes.
• Add “adopt-on-conflict” recovery for concurrent lane export hash mismatches by rebasing local snapped Version parents onto the remote lane heads and retrying export.
• Add early LaneId uniqueness validation before writing objects to disk, and improve export pending-dir cleanup on persist failures.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
scopes/scope/objects/objects/scope-index.ts	Adds a pre-write LaneId uniqueness validator and strengthens lane indexing against same-id/different-hash races.
scopes/scope/objects/objects/repository.ts	Reloads scope-index and runs LaneId uniqueness validation before persisting lane-related objects.
scopes/scope/export/export.main.runtime.ts	Ensures pending dirs are cleaned up when persistRemotes() fails to avoid stuck export queues.
scopes/git/ci/ci.main.runtime.ts	Reuses remote lanes across PR commits, merges main into PR lanes, and implements adopt-on-conflict export recovery for concurrent runs.
e2e/harmony/ci-commands.e2e.ts	Adds/updates E2E coverage for lane reuse, main→lane config propagation, and concurrent CI runner behavior.