feat: add local portable archive CLI

[larry-zy]

Related: #1421

Rationale for this change

Provide a local, operator-controlled logical archive for the default PowerContext SQLite deployment without adding remote archive storage or scope authorization.

What changes are included in this PR?

• Adds versioned .pcb export, inspect, dry-run validation, and confirmed restore commands.
• Preserves authoritative Source, Artifact, Memory, Candidate, and lineage records with checksums and immutable-identity conflict protection.
• Streams export and restore work, rebuilds local search projections, and documents the local SQLite boundary.
• Adds unit, CLI, large-fixture resource, and Runtime round-trip coverage.

Are there any user-facing changes?

Adds powercontext archive export, inspect, and restore for the SQLite database under POWERCONTEXT_HOME.

How was this change tested?

• make docs-test
• Focused Ruff and type checks
• Focused archive suite: 46 passed

AI usage statement

Codex (GPT-5) was used to assist implementation, tests, and documentation; changes were validated locally.

[Teingi]

resolve conflicts