docs: document error shape and table format breaking changes in CHANGELOG

Add entries for the error JSON shape change (new statusCode/suggestion
fields, message casing) and the plaintext table format change. Both are
breaking changes that should be called out for v3.0.

Made-with: Cursor

Author: nieblara

CHANGELOG.md

@@ -5,6 +5,8 @@
 ### ⚠ BREAKING CHANGES
 
 * When stdout is not a TTY, the default `--output` format is now **json** instead of plaintext. Scripts that assumed plaintext when output was piped or redirected should set `LD_OUTPUT=plaintext`, run `ldcli config --set output plaintext`, or pass `--output plaintext` (or `--output json` explicitly if you want JSON regardless of TTY). You can also set **`FORCE_TTY`** or **`LD_FORCE_TTY`** to any non-empty value to keep plaintext as the default when stdout is not a TTY, without changing the saved `output` setting.
+* Error responses now include `statusCode` (integer) and `suggestion` (string) fields in the JSON body. The `message` field for empty-body errors uses `http.StatusText` casing (e.g., `"Method Not Allowed"` instead of the previous `"method not allowed"`). If you parse error JSON from `ldcli`, update any assertions on the exact shape or casing.
+* Plaintext list output for `flags`, `projects`, `environments`, `members`, and `segments` now renders as aligned tables instead of `* name (key)` bullets. Singular resources render as key-value blocks. If you parse plaintext output programmatically, switch to `--output json`.
 
 ## [2.2.0](https://github.com/launchdarkly/ldcli/compare/v2.1.0...v2.2.0) (2026-02-20)