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/marmot/tests-extras.sh

@@ -271,7 +271,7 @@ test_14_wn_removes_a() {
   local deadline=$(( $(date +%s) + 120 )) removed=0
   while [[ $(date +%s) -lt $deadline ]]; do
     local show rc
-    show=$(HOME="$STATE_DIR" "$AMY_BIN" --name A --secret-backend plaintext --json \
+    show=$(HOME="$STATE_DIR" "$AMY_BIN" --account A --secret-backend plaintext --json \
               marmot group show "$a_gid" 2>&1)
     rc=$?
     printf '%s\n' "$show" >>"$LOG_FILE"