fix(named-agents): key editable rows by stable row key for uniqueness + save/remove identity

Draft rows (agent === null, id === null) previously keyed the other-names
exclusion and the live isNameTaken predicate by their nullable persisted id,
so a draft falsely collided with its OWN name (every name reported 'already
exists') and saving/removing one of multiple drafts could reconcile all of
them (a null agent captured identity matched every draft).

Identify rows solely by each Row's stable numeric `key` (already the
{#each} key) for: the other-names uniqueness hint, the controller's live
isNameTaken predicate, replaceAgent (save reconciliation), and removeRow.
A draft excludes itself exactly once; a persisted row keeps reconciling the
same row on later edits and no longer self-collides.

Add direct component-level regression tests (NamedAgentsView.test.ts) for
the self-collision, distinct/same-name multi-draft cases, saving-one-
updates-only-that-row, removing-one-removes-only-that-row, and post-persist
re-save reconciliation. 5 of 6 tests fail against the previous code (verified).

Verification: typecheck 0 errors, biome clean, 1252 tests pass, build ok.

0 files changed, 0 insertions, 0 deletions