import: grounded in Intuit's specs; atomic chart and bank imports

New vendored sources (docs/spec/sources/): Intuit's bank CSV upload and
IIF formats, ECMA-376 / Excel number storage, and the IRS form lines the
tax categories map to.

IIF export (rewritten to Intuit's IIF Import Kit):
- declares every account first (!ACCNT NAME, ACCNTTYPE, ACCNUM): an
  undeclared account is created in QuickBooks "as a new bank account";
  the MCP export types them (cash accounts BANK, the control accounts AR
  and AP, registered fixed assets FIXASSET, the rest by type);
- subaccounts by colon path, parents first; colons in a name replaced;
- ASCII only (IIF is ASCII text), dashes and quotes transliterated;
- the kit's 2007+ journal layout and M/D/YYYY dates; an entry using an
  undeclared account is refused.

Bank CSV:
- the 4-column layout is money out then money in by position, which
  matches Intuit's "Credit, Debit" and banks' "Debit, Credit" both (the
  doc's "Expense, Income" labels were wrong, the parsing was not);
- a slash date's order comes from the file (a part over 12 settles it)
  or the caller's new date_order, never a guess: Intuit recommends
  dd/mm/yyyy, US banks write mm/dd/yyyy;
- fractions of a cent and double negatives ("(-5)") are refused; the
  header is recognized on the first non-blank row.

Chart CSV: a blank code or name is refused with its row (found by the
new fuzz_import_csv target), and the core now refuses a blank account
code or name too (replay keeps older books).

MCP:
- books.import_chart_csv and books.import_bank_csv rehearse the whole
  file on a copy of the ledger first: a bad row anywhere refuses the
  file (before, a duplicate within the file, a parent after its child,
  or a date in a closed period left earlier rows behind);
- bank rules: the longest matching pattern wins (they arrive in a map,
  so "first match" changed from run to run).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

docs/spec/README.md

@@ -13,7 +13,8 @@ layers differ in what they cover and in whether we may copy them:
 | Layer | What it governs | Copyright | Here |
 |---|---|---|---|
 | **Pacioli (1494), Geijsbeek translation (1914)** | The mechanics of double entry: debits equal credits, the trial balance, one money, writing only forward, correcting by opposite entry, closing into capital. No modern standard restates these; they predate every regulator. | Public domain | Vendored verbatim: `sources/pacioli-1494.md` |
-| **IRS: Internal Revenue Code, Treasury Regulations, publications, form instructions** | Records and supporting documents, retention, accounting periods and methods, information returns (1099), capitalization (de minimis, 12-month rule), partners' capital, payroll taxes, rounding on returns | Public domain (17 U.S.C. §105; IRS.gov's content policy) | Vendored verbatim: `sources/irs-*.md`, `sources/us-public-domain-status.md` |
+| **IRS: Internal Revenue Code, Treasury Regulations, publications, form instructions** | Records and supporting documents, retention, accounting periods and methods, information returns (1099), capitalization (de minimis, 12-month rule), partners' capital, payroll taxes, rounding on returns, return line items for tax categories (`sources/irs-tax-lines.md`) | Public domain (17 U.S.C. §105; IRS.gov's content policy) | Vendored verbatim: `sources/irs-*.md`, `sources/us-public-domain-status.md` |
+| **File formats: Intuit (QuickBooks Online bank CSV, QuickBooks Desktop IIF), ECMA-376 Office Open XML, Microsoft Excel limits** | What `ledger-import` reads and writes: bank/card CSV layouts and signs, IIF journal entries, how XLSX stores numbers and Excel's 15-digit precision | © Intuit Inc.; © Ecma International; © Microsoft | Cited with short quotes, URLs, and hashes: `sources/intuit-bank-csv.md`, `sources/intuit-iif.md`, `sources/xlsx-numbers.md` |
 | **FASB Accounting Standards Codification (ASC)** | Authoritative US GAAP: cash flows (ASC 230), revenue and principal vs agent (ASC 606), foreign currency (ASC 830), credit losses and aging (ASC 326), property and depreciation (ASC 360) | © Financial Accounting Foundation | Cited by paragraph with short quotes only (in `rules.md`) |
 | **FASB Concepts Statement No. 8, Chapter 4 (2021)** | Definitions of the five elements (it replaced Concepts Statement 6) | © Financial Accounting Foundation; non-authoritative | Cited with short quotes only |
 | **Textbooks (OpenStax *Principles of Accounting, Vol. 1*)** | Conventions no standard states: normal balances, closing-entry mechanics, straight-line depreciation arithmetic | CC BY-NC-SA 4.0 (incompatible with this repo's license) | Cited with short quotes and attribution only |