Add ADR 0009 defining the unit / integration / e2e tiers by the seam
each exercises, with the value-returning vs process-side-effecting line
as the boundary between in-process and e2e-only. Add one line to ADR
0008 noting the Result seam is what makes error propagation assertable
in-process, cross-linking 0009.
Split the view command out of the entry point and make its failure a
value rather than an exception. index.ts is now scaffolding plus
dispatch; view.ts owns the behaviour, returning Result<string, ViewError>
(a plain-data tagged union) via neverthrow, with try/catch confined to a
readFile adapter. The entry point matches the Result at the boundary.
Because viewFile is a pure in-process function it is now unit-tested
directly (and counted by coverage), while the subprocess tests stay as
the end-to-end check. ADR 0008 records the errors-as-values convention.
