feat(reborn): add memory document storage boundary

[serrrfirat]

Summary

Draft carve-out for PR7 from the existing Reborn memory branch material.

Adds the first memory storage/backend substrate:

crates/ironclaw_memory
docs/reborn/contracts/filesystem.md
docs/reborn/2026-04-25-storage-catalog-and-placement.md

Includes:

• MemoryDocumentScope and MemoryDocumentPath for file-shaped memory documents;
• virtual /memory/tenants/{tenant}/users/{user}/projects/{project}/{path} paths;
• filesystem adapter that routes reads/writes/list/stat to a memory document repository;
• repository/source-of-truth split so search/index state is derived, not primary;
• in-memory repository/indexer fixtures for contract tests;
• DB-backed document repository surfaces for libSQL/Postgres feature configurations;
• tenant/user/project path isolation and traversal rejection.

Scope boundary

This intentionally does not wire production runtime memory behavior or expose user-visible behavior changes.

PR8 extends this branch with metadata/search/index/embedding/plugin seams and the agent-scoped path mapping that was present later in the old memory branch.

Verification

Passed locally:

cargo fmt --all -- --check
cargo test -p ironclaw_memory
cargo clippy -p ironclaw_memory --all-targets -- -D warnings
cargo test -p ironclaw_architecture
python3.11 scripts/check_no_panics.py --base origin/reborn-integration --head HEAD
bash scripts/pre-commit-safety.sh
git diff --check

Refs #2987.

[gemini-code-assist]

Code Review

This pull request introduces the ironclaw_memory crate, which provides filesystem adapters for memory documents, enabling virtual path access to database-backed storage. It includes repository implementations for PostgreSQL and libSQL that maintain compatibility with existing document schemas while enforcing tenant and project isolation. The PR also adds comprehensive documentation for the storage catalog and filesystem contracts, integrates the new crate into the workspace, and performs extensive dependency updates. I have no feedback to provide.