feat: add max-lines guard with self-cleaning exemptions (RD-02)

The dashboard refactor proved a page can be 42 lines. This rule holds
the rest of the app to that budget, before the split work in RD-20
through RD-26 begins.

Add max-lines at 250 (skipBlankLines, skipComments), scoped to
{apps,libs}/**/*.{page,component,section,step}.ts. The glob includes
section and step, the file kinds the dashboard refactor invented, so
new files from this arc do not escape the guard.

Add linterOptions.reportUnusedDisableDirectives: 'error' repo-wide.
ESLint 9 only warns on an unused disable by default, so a stale
exemption would not fail the build. At 'error', every later file
split must delete its own exemption or the build goes red.

Add a dated /* eslint-disable max-lines */ header to each of the
seven files that exceed the budget today, each with a reason and the
ticket that removes it. letter-canvas keeps its disable after RD-26,
because most of its lines are CSS and the rest is one letter.

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

libs/shared/src/ui/rich-text-editor/rich-text-editor.component.ts

@@ -1,3 +1,4 @@
+/* eslint-disable max-lines */ // toolbar + contenteditable logic in one component — removed by RD-21
 import { Component, ElementRef, computed, effect, input, output, viewChild } from '@angular/core';
 import { RichTextBlock, emptyBlock } from '@shared/kernel/rich-text';
 import { adjacentChip, createChip, readBlock, renderInto } from './rich-text-dom';