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-core/tests/invariants.rs

@@ -1423,8 +1423,14 @@ fn a_last_absorbs_close_gives_the_rounding_to_the_last_member() {
     let capital: Vec<AccountId> = ["3001", "3002", "3003"]
         .iter()
         .map(|code| {
-            l.add_account(code, "Capital", AccountType::Equity, None, false)
-                .unwrap()
+            l.add_account(
+                code,
+                &format!("Capital {code}"),
+                AccountType::Equity,
+                None,
+                false,
+            )
+            .unwrap()
         })
         .collect();
     let e = l.create_entry(date(5), "sale");