feat: persist DuckLake object-table writes with rollback cleanup

[weicao]

Summary

Replay accepted object-storage candidate 450fe6f0 onto current main (7a587430). Unique parent is exact main. Does not update PR #489 / task75-object-table.

This PR is the first-cut DuckLake object-table delivery: persist storage selection, dual-protocol writes, rollback compensation, and failure cleanup. Shutdown coordination is already on main via #492.

Usage boundaries (must keep)

1. MySQL CREATE TABLE is an implicit commit and is not undone by ROLLBACK (local and object tables alike).
2. One transaction cannot write both a local table and an object table (1105). Unsupported, not omitted.
3. The local DuckLake catalog must persist. The object bucket stores table data only; losing the catalog cannot be recovered from the bucket alone.

Identity

• Replay source: 450fe6f0aeee72c7c008b44ea57e8adae0815f52
• Base: 7a58743079680cf05f35fc1e97f531a0cba5e7f7
• FlightSQL constructor kept NewSQLiteFlightSQLServerWithProvider
• No diagnostic inject env / DIAG_RAW dumps
• Docs: docs/object-storage.md

Product acceptance on 450fe6f0 / image sha256:8c8ed995…cd719 stays; this PR only needs review of the main integration diff. No v0.2.1 / latest change.

[leon-ape]

Independent review of exact head d73a66f039eb075a3633ac89f2661fd0424c2c1d.

• Unique parent fb299713d6685e3ff63832e9517b6373e0dd1053; GitHub verification valid.
• Diff vs parent is only docs/object-storage.md: candidate id 450fe6f0 and must not include restored; three usage boundaries remain.
• Product files vs accepted 450fe6f0 unchanged except the already-reviewed FlightSQL idempotent close. No inject/DIAG_RAW.
• Reuse FlightSQL Python SUCCESS on fb299713 (job 101608295902); this head does not change that source.

APPROVE binds only this OID. Task #78 product acceptance is not reopened. No v0.2.1 / latest change.

[leon-ape]

Independent review of exact head 6106a18fa05e32aa3d3d923141d6d68d3e04dbf0.

• GitHub verification valid.
• Unique parent 7a58743079680cf05f35fc1e97f531a0cba5e7f7.
• Tree 65bdc21bbed281a6c19808ab3525183585b7d17b equals previous head d73a66f039eb075a3633ac89f2661fd0424c2c1d.
• Single commit; not an empty signed follow-up.

APPROVE binds only this OID. Go/Dolt historical reds not re-verified. Task #78 not reopened. No v0.2.1 / latest change.