Fixed assets, fully featured: tags, serials, acquisition links, label sheets, the fixed asset register, and an Assets section in the viewer; fix a flaky verify

- core: asset tags (generated PREFIX-0001 or the human's own; unique ignoring case; never reused by another asset) and serial numbers (rules.md B-24); a journaled link from an asset to the entry that acquired it (posted, unreversed, debiting the cost account); fixed_asset_register(as_of), reconciled to the GL (unposted depreciation, unregistered cost)
- store: asset.tagged, asset.serial_set, asset.acquisition_linked journaled, replayed, projected (schema v9); differs_from now also compares control roles and tag history
- config: [books] asset_tag_prefix, default the company's initials without legal-form words
- import: Avery 5160/8160 label sheets with QR codes (geometry vendored from Avery, docs/spec/sources/avery-5160.md); the register as XLSX and PDF
- mcp: register_asset tags (and links) automatically; books.label_asset, books.asset_labels; asset tools take a tag; books.show asset / assets page / register report; export fixed_asset_register (json, csv, xlsx, pdf) and in the CPA package
- viewer: Assets page (register, reconciliation), asset page (identity, schedule posted vs not, entries, documents), Fixed asset register report, global search by tag/serial/description, journal text, needs-attention items
- fix: verify compared snapshot amounts as strings; a zero total summed in hash-map order could print "0" or "0.00", so agreeing books failed verify at random. Now by value (regression test)
- tests: spec-blind suites for tags, register, prefix, store, MCP; label and register PDF/XLSX tests; viewer tests

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

crates/ledger-core/src/error.rs

@@ -116,6 +116,41 @@ pub enum LedgerError {
         placeholder: bool,
     },
 
+    /// An asset tag of the wrong form (see `assets::check_asset_tag`).
+    #[error("bad asset tag {tag:?}: {why}")]
+    InvalidAssetTag {
+        /// The tag given.
+        tag: String,
+        /// Why it was refused.
+        why: String,
+    },
+
+    /// Asset tags are never shared or reused: another asset holds, or
+    /// held, this one.
+    #[error("asset tag {tag:?} belongs to asset {asset}; tags are never reused, so choose another")]
+    AssetTagTaken {
+        /// The tag given.
+        tag: String,
+        /// The asset that holds or held it.
+        asset: u64,
+    },
+
+    /// An asset's acquisition entry must be a posted, unreversed entry
+    /// that debits the asset's cost account.
+    #[error("entry {entry} can't be asset {asset}'s acquisition: {why}")]
+    AcquisitionEntryMismatch {
+        /// The asset.
+        asset: u64,
+        /// The entry given.
+        entry: u64,
+        /// Why not.
+        why: String,
+    },
+
+    /// A serial number of the wrong form (see `assets::check_serial`).
+    #[error("bad serial number: {0}")]
+    InvalidSerial(String),
+
     /// No control role has that name (see `ledger_core::control_accounts`).
     #[error(
         "no role {0:?}; the roles are receivables, revenue, payables, general_expense, \