Fixed assets carry federal tax basis beside book value; tests sweep stale temp dirs

- core: TaxBasisRule (cost IRC 1012, carryover IRC 723, personal-use conversion Treas. Reg. 1.168(i)-4(b)), TaxBasis with the contributor's adjusted basis, Asset::tax_basis and ::built_in_gain (IRC 704(c)); the register gains tax rule, contributor basis, tax basis, built-in gain, total tax basis, missing count (rules.md B-25; sources vendored in docs/spec/sources/irs-partnership-basis.md)
- store: asset.tax_basis_set journaled, replayed, projected (schema v10)
- mcp: books.set_asset_tax_basis; register_asset takes tax_basis_rule and contributor_basis, checked before anything registers (found by the spec-blind suite); list_assets and the register export (json, csv) carry tax basis; instructions say to record it for every asset
- import: the register's XLSX and PDF gain the federal tax basis table with citations
- viewer: tax basis on the Assets page, the asset page (a Tax basis card), the report, the journal, and Needs attention for assets without one
- just: check and the mutation recipes sweep this user's test book dirs older than an hour (killed runs had left 23 GB in RAM-backed /tmp)
- docs: the parties, attachments, TIN vault, completeness engine, and updates designs (docs/parties-and-attachments.md)
- tests: spec-blind tax basis suites in core, store, MCP; register PDF/XLSX and viewer tests

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

crates/ledger-core/tests/spec_assets_payroll.rs

@@ -61,6 +61,7 @@ fn asset(cost: &str, salvage: &str, life: u32, purchase: NaiveDate) -> Asset {
         tag: None,
         serial: None,
         acquired_by: None,
+        tax: None,
     }
 }