docs(W4): revert the NORTH_STAR.md stamp; a projection cannot carry a hand-added header

Found by vision's adversarial pass (W5) and re-measured here. The finding was raised as
latent; it is live in this PR.

docs/fleet/NORTH_STAR.md is generated by renderNorthStarMarkdown()
(packages/mosaic/src/commands/fleet.ts:373), whose first emitted line is the H1 and which
emits no front matter at all. fleet-north-star.spec.ts:110-114 is a drift test that reads
the committed file from disk and asserts full-string equality against the renderer output:

    expect(rendered).toBe(committed);

Stamping the file changed line 1 from '# Mosaic Fleet - NORTH STAR' to '---', so the
assertion fails. vitest could not be run in this worktree (node_modules empty, 'Cannot find
package yaml'), which is a harness gap and not a test result, so this is shown by
construction: the assertion above, the renderer's first lines.push, and line 1 before
versus after.

Reverted to origin/next verbatim: git diff origin/next -- docs/fleet/NORTH_STAR.md is 0
lines. Control on docs/fleet/reference/cli.md returns 13 lines, so the diff command does
report differences when they exist.

The header for a projection has to come from the renderer, not the file. That is a code
change and belongs in the flatten PR beside the resolveNorthStarPaths() fix.

Stamped count 104 -> 103. Untouched 23 -> 24. Worklist records it as a fourth held row.

docs/fleet/NORTH_STAR.md

@@ -1,8 +1,3 @@
----
-kind: projection
-status: active
----
-
 # Mosaic Fleet — NORTH STAR
 
 > **Generated file — do not edit by hand.**