fix(store): derive current-schema column expectations from the applied schema

[rodboev]

Docbank now derives current-vault column validation from the same embedded schema that creates the vault. Adding a column to one of the six guarded tables no longer requires a second expected-column list, so a fresh vault can reopen without losing the exact layout guard.

The check still rejects foreign columns, and released schema adapters, JSONL cutovers, schema versions, and future-version refusal remain unchanged. Each validation derives the current layout through the SQLite driver used for the vault, so drivers with the same display name cannot reuse another driver's expectations.

[roborev-ci]

roborev: Combined Review (e7d0a2a)

Verdict: One medium-severity cache-keying issue was identified; otherwise, the changes appear sound.

Medium

• internal/store/upgrade.go:264 — The schema cache is keyed only by driver.Name() and schemaSQL. Custom drivers with the same name but different schema-affecting behavior may incorrectly reuse cached expectations, causing valid vaults to be rejected. Avoid the global cache or include a stable identity/configuration capturing the driver’s behavior.

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Reviewers: 2 done | Synthesis: codex, 6s | Total: 4m12s

[roborev-ci]

roborev: Combined Review (86f3888)

No issues found.

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Reviewers: 2 done | Synthesis: codex | Total: 3m47s