feat: add iFlow CLI support (#1875)

Add `iflow` as a supported AI agent (the key users pass to --ai) across
all relevant configuration files, release scripts, agent context
scripts, and README. Includes consistency tests following the same
pattern as kimi/tabnine additions.

- README: describe `check` generically (git + all AGENT_CONFIG CLI agents)
- README: describe `--ai` with reference to AGENT_CONFIG for full list

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/specify_cli/__init__.py

@@ -289,6 +289,13 @@ AGENT_CONFIG = {
         "install_url": "https://www.npmjs.com/package/@mariozechner/pi-coding-agent",
         "requires_cli": True,
     },
+    "iflow": {
+        "name": "iFlow CLI",
+        "folder": ".iflow/",
+        "commands_subdir": "commands",
+        "install_url": "https://docs.iflow.cn/en/cli/quickstart",
+        "requires_cli": True,
+    },
     "generic": {
         "name": "Generic (bring your own agent)",
         "folder": None,  # Set dynamically via --ai-commands-dir