P3: rename accounts, one set of period defaults, tax categories warn or refuse (defects 15, 16, 8)

books.rename_account; account names trimmed, bounded, refused when a
sibling's or TIN-shaped; books.show refuses what its target ignores. A
report asked for without dates covers this fiscal year so far, everywhere
(one rule for tools, descriptions and the viewer; the IIF and CPA package
keep their own dates). policy.require_tax_category warns or refuses; a
Form 4797 gain is shown apart on every return.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-mcp/tests/spec_mcp.rs

@@ -746,6 +746,10 @@ fn happy_path(name: &str) -> Mcp {
         "books.renumber_account",
         json!({"account": "7000", "code": "7100"}),
     );
+    m.ok(
+        "books.rename_account",
+        json!({"account": "7100", "name": "Gain or Loss on Sale", "reason": "clearer"}),
+    );
     m.ok("books.settings", json!({}));
     m.ok("books.roles", json!({}));
     m.ok(