Fix code-review findings across domain, persistence, server and frontend

Full-codebase review turned up five real correctness/security bugs and
a dozen smaller inconsistencies; all are fixed here with matching test
coverage:

- BMK uniqueness silently allowed German-umlaut duplicates ("Ä1" vs
  "ä1") because the DB's normalized index only folds ASCII case. Added
  a shared Unicode-aware pre-check used by every circuit/component
  insert and rename path (one of which had no pre-check at all).
- CircuitDeviceRow.simultaneityFactor had no upper bound at the row
  level (command model and snapshot/restore schema), unlike every
  sibling entity, letting a bad value silently corrupt power totals.
- Grid cell editing silently misread German thousands-separator input
  ("1.500" parsed as 1.5); "." is now rejected outright with a clear
  message instead of guessing.
- The editor's shared command runner (runCommand/applyHistory) had no
  re-entrancy guard, so a double click/drop could fire the same
  command twice and race a BMK collision or revision conflict. Added a
  synchronous ref guard plus isSaving on the buttons that lacked it.
- GET .../next-identifier leaked circuit-numbering state for sections
  in other projects (no ownership check, 400 instead of 404). Moved
  under /projects/:projectId and scoped it.

Also: added the missing circuits.section_id / circuit_device_rows.
circuit_id indexes (migration 0006), gave FormModal a focus trap /
Escape-to-close / focus restore and rebuilt ProjectSettingsModal on
top of it instead of duplicated markup, removed dead code (3 orphaned
domain model files, an unused persistence helper, a wrapper only used
by its own test), pointed the project page at GET /projects/:id
instead of listing+filtering client-side, closed the gap between the
documented 18 MB CSV limit and the ~17.17 MiB actually enforced, added
missing upper bounds on several free-text fields, filled in nine
missing German labels in the revision timeline, replaced a
key-order-fragile JSON.stringify equality check with a real field
comparison, made an implicit sort-order assumption in three
renumbering helpers explicit, cleared the sidebar's target selection
when it no longer resolves after a tree reload, and fixed
updateGlobalDevice to check-then-write instead of write-then-check.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/circuit-grid-model.test.ts

@@ -187,12 +187,25 @@ describe("circuit grid model", () => {
   });
 
   it("parses numeric drafts and rejects invalid values", () => {
-    assert.equal(parseNumeric("quantity", " 2.5 "), 2.5);
+    assert.equal(parseNumeric("quantity", " 1500 "), 1500);
     assert.equal(parseNumeric("powerPerUnit", " 1,25 "), 1.25);
     assert.equal(parseNumeric("quantity", ""), undefined);
     assert.throws(() => parseNumeric("quantity", "two"), /Ungültiger Zahlenwert/);
   });
 
+  it("rejects a dot instead of silently misreading it as a thousands separator", () => {
+    // "1.500" typed with German thousands-separator intent (meaning 1500)
+    // must never silently become 1.5 — it must fail loudly instead.
+    assert.throws(
+      () => parseNumeric("cableLength", "1.500"),
+      /Dezimalstellen mit Komma eingeben/
+    );
+    assert.throws(
+      () => parseNumeric("powerPerUnit", "2.5"),
+      /Dezimalstellen mit Komma eingeben/
+    );
+  });
+
   it("builds nullable circuit command patches from grid drafts", () => {
     assert.deepEqual(buildCircuitEditPatch("voltage", ""), {
       voltage: null,