feat: declarative backend Suitefile compiler and drift-safe sync

[cmdr-chara]

Problem

Backend tests can be created and updated individually, but a repository cannot currently declare an entire dependency-aware TestSprite suite as reviewable source. Teams must manually keep remote test metadata, Python code, and produces/consumes relationships aligned. That makes drift, accidental duplication, and unsafe bulk maintenance difficult to detect before mutation.

Proposed CLI surface

Add a versioned backend Suitefile and four commands:

• testsprite suite validate <manifest> validates the manifest, referenced Python files, and dependency graph locally.
• testsprite suite graph <manifest> emits deterministic execution waves compiled from produces/consumes declarations.
• testsprite suite plan <manifest> compares desired state with the remote project without mutation.
• testsprite suite apply <manifest> --confirm creates or updates the reviewed changes.

An adjacent lockfile records stable suite-key to remote-test identity, code version, desired-state hash, and any pending idempotent create request.

Safety boundaries

• Schema v1 manages backend tests only.
• Unknown fields, cycles, ambiguous or missing producers, duplicate identities, oversized code, and lexical/symlink path escapes fail locally.
• Existing remote tests are adopted only by explicit testId or lockfile identity; same-name tests are conflicts.
• Unmanaged remote tests are reported and never deleted.
• Mutations require --confirm, use deterministic idempotency keys, and retain interrupted-create identity for safe replay.
• Optimistic concurrency protects code updates.
• No new runtime dependencies or outbound services are introduced.

Relationship to #125 / PR #265

PR #265 round-trips one test definition at a time. This proposal is complementary: it compiles a multi-test dependency graph and reconciles a repository-owned desired state against a project. It does not depend on or replace test export / test import.

Acceptance criteria

• Local validation and graph compilation require no credentials or network.
• Plan output classifies each managed test as create, update, unchanged, or conflict.
• Apply refuses conflicts and unconfirmed mutations.
• Lockfile writes are atomic and interrupted creates are replay-safe.
• CLI help, documentation, unit tests, and package output include the new command group.

A tested implementation is ready on a contributor branch; I am opening this issue to satisfy the repository's feature workflow and am happy to adjust the contract during review.

[cmdr-chara]

/assign

[testsprite-hob]

Assigned to @cmdr-chara. Thanks for taking this on. (2 more slots available.)

Your open assigned issues (1/3):
(none)

[zeshi-du]

Closing with the PR — see the full verdict on #269. Short version: suite/testlist capability is server-owned and its CLI surface is scheduled as a facade over that (quota-first); a client-side compiler pre-empts it in the wrong layer. The declarative-definition UX signal is registered in the internal workstream.