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/agents.py

@@ -147,6 +147,12 @@ class CommandRegistrar:
             "format": "markdown",
             "args": "$ARGUMENTS",
             "extension": ".md"
+        },
+        "iflow": {
+            "dir": ".iflow/commands",
+            "format": "markdown",
+            "args": "$ARGUMENTS",
+            "extension": ".md"
         }
     }