Add research context and artifact ingestion

[foxsplendid]

What changed

• Add atomic ingestion for parsed-paper/1.0, reading-note/1.0, review/1.0, and lineage-graph/1.0.
• Add the bounded, read-only Context Capsule CLI and MCP entry.
• Add Windows path, Junction/reparse, lock, identity, path-redaction, and concurrency safeguards.
• Synchronize the v0.18.0 product and trust documentation.

Why

Researchers need a recoverable project context that keeps reviewed state separate from reference-only literature hints, while local artifact ingestion must remain deterministic, private, and safe under ordinary filesystem races.

Product impact

The new capsule supports the session-start resume flow. Research artifacts remain reference-only until reviewed. This release does not claim runtime support for experiment-run/1.0 or claim-evidence/1.0.

Validation

• 302 tests passed, 4 permission-dependent file-symlink tests skipped.
• Real Windows Junction tests passed.
• Public-tree and private-marker scans passed.
• Independent review found no P0/P1 issue.

Merge note

The umbrella candidate pins commit 6380bb0a8bfe8129a9edb2f903856a33b59dbcbb. Preserve this commit SHA with a merge commit or fast-forward; do not squash or rebase this PR.