feat(pricing): implement pricing comparison table UI

[Deb-Auth]

Summary

Implements the detailed feature comparison table for the pricing page. Visitors can now compare every capability across the four tiers in one place instead of cross-referencing the individual plan cards.

closes #397

What was added

frontend/app/pricing/components/PricingTable.tsx

• A PricingTable component rendering a four-column comparison table (Free, Personal, Business, Enterprise).
• Features are mapped to their respective tiers through a typed data model:
  • PricingTierColumn describes a plan column (name, price label, popular flag, CTA).
  • PricingFeature.values is a Record<PricingTierId, PricingFeatureValue>, so TypeScript enforces that every feature declares a value for every tier and the table can never go ragged.
  • A value is either a boolean (renders an availability icon) or a string (renders a quota/limit such as "Unlimited", "Testnet", "10").
• Features are grouped into five sections that mirror the product surface: Verification, Certificates, Collaboration, Developer and Support. Feature values were derived from the tier feature lists already declared on the pricing page so the table and the cards stay consistent.
• Tier columns and feature groups are exported (PRICING_TIER_COLUMNS, PRICING_FEATURE_GROUPS) and can be overridden through props, which keeps the component reusable and testable.

frontend/app/pricing/page.tsx

• Renders the table between the plan cards and the FAQ section.

Design and accessibility notes

• Semantic table markup: <caption> (screen-reader only), scope="col" on tier headers, scope="row" on feature headers, and scope="colgroup" on group separator rows.
• Boolean cells pair an aria-hidden icon with an "Included" / "Not included" screen-reader label, so the table is not conveyed through iconography alone.
• The container scrolls horizontally on narrow viewports while the feature column and the tier header stay pinned, so the row context is never lost.
• The "Personal" column carries the same "Most Popular" highlight used by the pricing cards.
• Styling follows the existing pricing page conventions (Tailwind, primary/darkblue theme tokens, light and dark mode).

Tests

Added frontend/app/pricing/components/__tests__/PricingTable.test.tsx covering:

• a column header renders for every tier;
• every feature group and feature row renders;
• each feature maps to the correct per-tier value, for both string and boolean cells;
• the popular tier badge renders;
• each tier renders a CTA link pointing at the right destination.

Test Suites: 1 passed, 1 total
Tests:       5 passed, 5 total

pnpm --filter web run lint reports no new errors or warnings from these files.

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