fix(cli): rename global --name to --account to free --name for subcommands

The marmot harness surfaced the bug on first run: amy stripped
`marmot group create --name "Interop-02"` thinking the global
account selector ran into the group's display-name flag. Result:
amy resolved the "Interop-02" account, found no identity.json, and
errored — no group ever got created.

Renames the global account-selector flag to `--account`. The per-
subcommand `--name` flags (`marmot group create --name "Demo"`,
`profile edit --name "Alice"`, `marmot await group --name X`) are
untouched — they're free of the global parser now that it doesn't
claim the same name.

Sweep:
- `Main.kt`: GlobalFlag.NAME → ACCOUNT, long "--account".
- `Config.kt`: DataDir.resolve param renamed nameFlag → accountFlag;
  every error message points the user at --account.
- `UseCommand.kt`: error hint says `amy --account NAME init`.
- All test wrappers + direct $AMY_BIN calls under cli/tests/ swap
  the global `--name X` for `--account X` (subcommand --name kept
  exactly where it appeared).
- README + DEVELOPMENT updated.

cli/tests/cache/cache-headless.sh

@@ -83,7 +83,7 @@ source "$TESTS_DIR/headless/helpers.sh"
 # shellcheck source=../dm/setup.sh
 source "$TESTS_DIR/dm/setup.sh"
 
-amy_b() { HOME="$STATE_DIR" "$AMY_BIN" --name B --secret-backend plaintext --json "$@"; }
+amy_b() { HOME="$STATE_DIR" "$AMY_BIN" --account B --secret-backend plaintext --json "$@"; }
 
 # Helper: B-side amy_json. The dm headless's helpers.sh hardcodes A_DIR
 # in amy_a; we need a parallel for B without re-sourcing.
@@ -251,7 +251,7 @@ fi
 # ----------------------------------------------------------------------
 banner "T7 — store maintenance verbs (sweep/scrub/compact) on an empty store"
 TMP_HOME=$(mktemp -d)
-T7_AMY=(${AMY_BIN} --secret-backend plaintext --name throwaway --json store)
+T7_AMY=(${AMY_BIN} --secret-backend plaintext --account throwaway --json store)
 T7_STAT=$(HOME="$TMP_HOME" "${T7_AMY[@]}" stat)
 T7_SWEEP=$(HOME="$TMP_HOME" "${T7_AMY[@]}" sweep-expired)
 T7_SCRUB=$(HOME="$TMP_HOME" "${T7_AMY[@]}" scrub)