viewer: hide the `raw/` layer (it dumps competitor snapshots + .prev diff files as documents)

[nmrtn]

Found by dogfooding the wiki migration on nanopm's own repo.

After migration, the macOS viewer lists every file under .nanopm/raw/ as an individual document under DISCOVER — competitor snapshots (api_docs.md, changelog.md, other.md), their .prev diff-history files, and the Intel-* reports. On this repo that's 30+ junk entries, making the sidebar look like chaos right after migration.

Per the schema, raw/ is the immutable source layer — it should never be browsed or surfaced as wiki pages (only wiki/ pages are documents). The intel/ → raw/competitors/ relocation moved these into raw/, but the viewer's ArtifactScanner / PhaseMapper still maps them to a phase and shows them.

Fix: the viewer should skip everything under .nanopm/raw/ (it's sources, not pages). Competitor reports can still surface via the existing Competitors section if desired, but the raw snapshots and .prev diff files must not be listed as documents.

Impact: the visual "this is a mess" reaction to the wiki is mostly this bug — with raw/ hidden, the sidebar collapses from ~40 entries to the real ~18 (docs + opportunities + competitors).