feat(cli): suggest the nearest module name on not-found ("did you mean?")

[grantcarthew]

Summary

When a module identifier resolves to nothing, suggest the single nearest known
module name instead of a bare "not found". This supersedes the original idea in
this issue (auto-trying plural/singular variants of the search terms) with a more
general, lower-risk approach: a non-binding "did you mean?" hint computed by edit
distance over the candidate names the surface already gathers.

The original report: start task modules/role/create fails because the real name
is module/role/create (singular). A nearest-name suggestion fixes that case and
every other near-miss — typos, a wrong path segment, a transposition — with one
mechanism, without making resolution itself fuzzy.

Why not auto-plural

+s/-s only handles regular plurals (it misses category/categories), and
auto-resolving a guessed variant could silently install or act on the wrong
module. Edit-distance suggestion keeps resolution strictly literal and
deterministic while covering far more slips, and a wrong suggestion costs nothing
because it never acts on its own.

Behaviour

• On a confirmed not-found (registry reachable), compute the edit distance from
  the query to the in-scope candidate names and print the single closest if it is
  within a threshold.
• Suggestion only. Nothing auto-resolves or auto-installs. Exit codes and
  not-found semantics are unchanged; the literal resolution contract is untouched.
• Top-1, with a length-relative threshold and a deterministic (lexical) tie-break.
• Do not suggest when the registry was unreachable (the transient/retry path): the
  candidate pool is incomplete and cannot be trusted.
• Skip suggestions for very short queries where edit distance is not meaningful.

Scope

This assumes the candidate-gathering unification (project
05-unify-candidate-gathering.md) is in place, so the suggester attaches once per
surface and covers every module-selecting surface: the resolution surfaces
(task, --role, --context, --agent, get/describe), uninstall /
config remove, config get, install, and update. search benefits too
wherever it returns zero results.

Implementation notes

• Edit distance via a copied-in copy of agnivade/levenshtein. Case-fold both
  inputs first (the library is case-sensitive). It is plain Levenshtein, so an
  adjacent transposition costs 2 — size the threshold accordingly.
• License handling for the copied file is a maintainer action item, deliberately
  deferred (the file is copied without its license header for now).
• The path separator / is an ordinary character to the metric, so a
  segment-boundary slip like modules/role/create vs module/role/create is
  distance 1 with no need to split on /.

Acceptance

• start task modules/role/create prints a suggestion for module/role/create
  and still exits as not-found.
• Garbage input with nothing within the threshold prints no suggestion.
• Successful resolution and all exit codes are unchanged.