workspace: memory content mirrored to cloud is unfiltered — no secret/PII redaction

Found during v0.9.7 release review (Chaos Gremlin/Privacy Auditor persona).

`memory-extract.ts`'s tool description explicitly invites the agent to capture 'warehouse configs found via /discover, query patterns from sql_optimize, naming conventions observed' into memory blocks. Nothing in the write path (`memory-write.ts`, `memory-extract.ts`) or the mirror path (`memory-sync.ts`'s `push()` forwards `block.content` verbatim to `MemoryApi.add/update`) does secret-scanning, PII filtering, or redaction before content leaves the machine (when workspace mirroring is enabled).

Compounds the disclosure gap fixed in v0.9.7 (see bind-time consent line added in workspace.tsx/link.ts): once a user knows memory syncs and accepts that, there's still no guardrail preventing a warehouse connection string or customer-identifying value from being captured into a block and mirrored.

Deferred because this needs a content-scanning/redaction design (not a quick patch), and the feature remains gated behind the off-by-default `ALTIMATE_WORKSPACE` pilot flag.

Trace the memory write and mirror paths in memory-write.ts, memory-extract.ts, and memory-sync.ts, especially push() forwarding block.content to MemoryApi.add/update. Review the consent-related changes in workspace.tsx and link.ts for context. Done requires an agreed content-scanning and redaction design that prevents secrets and PII from leaving the machine when mirroring is enabled.

索引モデルが issue の本文から書いたものです。