docs: align README/INSTALL/AGENTS with system-anatomy canon
Replace surveillance-flavored verbs in owner-facing prose ("captures
screen and audio", "screen and audio capture works", "capture source")
with the system-anatomy canon's co-experience phrasing
("experiences your screen and audio along with you"). solstone-linux
is now framed in AGENTS.md project-overview prose as one of the
trinity's observers.
Add a "Brand canon" section to AGENTS.md pointing to
~/projects/extro/cmo/brand/system-anatomy.md, naming the banned
verbs in branded copy, and clarifying that internal architecture
vocabulary (the Capture loop, capture pipeline, module names) is
canon-permitted in code-only contexts and stays as-is.
Internal capture-loop references in AGENTS.md (lines 19, 40, 46, 69)
are unchanged. CLAUDE.md remains a symlink to AGENTS.md and rides
automatically. No source, test, or config changes.
Mirrors the precedent sweeps in the parent solstone repo
(commits ddec60d5 and 929448de).