feat: tax categories and the tax summary report

wanderbooks is a general MCP-first accounting application: every
business needs its accounts mapped to where they land on its income tax
return, and its CPA needs book-to-tax differences surfaced, not hidden.

- ledger_core::tax: a catalog of stable categories (gross_receipts,
  commissions_fees, meals, guaranteed_payments, officer_compensation,
  nondeductible, ...) with kind (income, cost of goods, deduction), the
  returns each appears on (Schedule C, 1065, 1120-S, 1120), a default
  deductible percent (meals 50, nondeductible 0), and guidance. Keys,
  not line numbers: form lines move from year to year.
- Accounts carry tax_category and an optional deductible_percent
  override, validated against the account type (and the return, at the
  MCP layer), journaled as account.tax_set, replayed, projected (schema
  v6).
- tax_summary(start, end, form): the P&L grouped by category, book and
  deductible amounts (half away from zero to the cent), contra income
  (refunds) reducing receipts, and every account still uncategorized.
- MCP: books.tax_categories (filtered to the configured return),
  books.set_tax_category, a tax_summary report in every format and in
  the CPA package, chart output with categories, and a fifth
  tax_category column in chart CSV imports, validated before anything is
  created. [company] tax_form, or derived from tax_classification.

Scope stays book basis: no tax depreciation, basis, or filing.

Tests: a hand-computed quarter (50% meals 333.33 -> 166.67, penalties at
0%, refunds as negative receipts, guaranteed payments, one uncategorized
account; book net 5,276.67 vs tax 5,483.33); overrides; category/account
/return validation; form parsing and derivation; CSV parsing; stdio:
filtered catalog, mapping, refusal, summary, all-or-nothing import.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

crates/ledger-store/src/store.rs

@@ -1789,6 +1789,30 @@ impl Store {
         Ok((id, sha, dedup))
     }
 
+    /// Set (or clear) an account's tax category and deductible percent.
+    /// Journaled as `account.tax_set`.
+    pub fn set_account_tax(
+        &mut self,
+        account: AccountId,
+        category: Option<&str>,
+        deductible_percent: Option<Decimal>,
+    ) -> Result<(), StoreError> {
+        self.ledger
+            .check_account_tax(account, category, deductible_percent)?;
+        let line = self.append_journal(
+            "account.tax_set",
+            json!({
+                "account_id": account,
+                "tax_category": category,
+                "deductible_percent": deductible_percent.map(|p| p.to_string()),
+            }),
+        )?;
+        self.ledger
+            .set_account_tax(account, category, deductible_percent)?;
+        apply_line_to_sqlite(&self.conn, &line)?;
+        Ok(())
+    }
+
     /// Link a previously filed (unlinked) receipt to an entry. A receipt
     /// already linked elsewhere must be unlinked first, so moving evidence
     /// off an entry always goes through [`Store::unlink_receipt`] and its
@@ -2712,6 +2736,19 @@ fn replay_line_into_ledger(
                 )));
             }
         }
+        "account.tax_set" => {
+            let pct = match p.get("deductible_percent").and_then(|v| v.as_str()) {
+                Some(s) => Some(s.parse().map_err(|_| {
+                    StoreError::JournalCorrupt("account.tax_set deductible_percent".into())
+                })?),
+                None => None,
+            };
+            ledger.set_account_tax(
+                get_u64(p, "account_id")?,
+                p.get("tax_category").and_then(|v| v.as_str()),
+                pct,
+            )?;
+        }
         "receipt.attached"
         | "receipt.linked"
         | "receipt.unlinked"
@@ -3074,6 +3111,16 @@ fn apply_line_to_sqlite(conn: &Connection, line: &JournalLine) -> Result<(), Sto
                 ],
             )?;
         }
+        "account.tax_set" => {
+            conn.execute(
+                "UPDATE accounts SET tax_category = ?, deductible_percent = ? WHERE id = ?",
+                params![
+                    p.get("tax_category").and_then(|v| v.as_str()),
+                    p.get("deductible_percent").and_then(|v| v.as_str()),
+                    get_u64(p, "account_id")? as i64,
+                ],
+            )?;
+        }
         "receipt.unlinked" => {
             conn.execute(
                 "UPDATE attachments SET entry_id = NULL WHERE id = ?",