chore: ZXDB env validation, MySQL setup, API & UI

This sanity commit wires up the initial ZXDB integration and a minimal UI to explore it.

Key changes:
- Add Zod-based env parsing (`src/env.ts`) validating `ZXDB_URL` as a mysql:// URL (t3.gg style).
- Configure Drizzle ORM with mysql2 connection pool (`src/server/db.ts`) driven by `ZXDB_URL`.
- Define minimal ZXDB schema models (`src/server/schema/zxdb.ts`): `entries` and helper `search_by_titles`.
- Implement repository search with pagination using helper table (`src/server/repo/zxdb.ts`).
- Expose Next.js API route `GET /api/zxdb/search` with Zod query validation and Node runtime (`src/app/api/zxdb/search/route.ts`).
- Create new app section “ZXDB Explorer” at `/zxdb` with search UI, results table, and pagination (`src/app/zxdb/*`).
- Add navbar link to ZXDB (`src/components/Navbar.tsx`).
- Update example.env with readonly-role notes and example `ZXDB_URL`.
- Add drizzle-kit config scaffold (`drizzle.config.ts`).
- Update package.json deps: drizzle-orm, mysql2, zod; devDeps: drizzle-kit. Lockfile updated.
- Extend .gitignore to exclude large ZXDB structure dump.

Notes:
- Ensure ZXDB data and helper tables are loaded (see `ZXDB/scripts/ZXDB_help_search.sql`).
- This commit provides structure-only browsing; future work can enrich schema (authors, labels, publishers) and UI filters.

Signed-off-by: Junie@lucy.xalior.com

AGENTS.md

@@ -0,0 +1,121 @@
+# AGENT.md
+
+This document provides an overview of the Next Explorer project, its structure, and its implementation details.
+
+## Project Overview
+
+Next Explorer is a web application for browsing and exploring the registers of the Spectrum Next computer. It is built with Next.js (App Router), React, and TypeScript.
+
+The application reads register data from `data/nextreg.txt`, parses it on the server, and displays it in a user-friendly interface. Users can search for specific registers and view their details, including per-register notes and source snippets.
+
+## Project Structure
+
+The project is a Next.js application with the following structure:
+```
+
+next-explorer/
+├── eslint.config.mjs
+├── next.config.ts
+├── package.json
+├── pnpm-lock.yaml
+├── tsconfig.json
+├── data/
+│   ├── nextreg.txt
+│   ├── custom_parsers.txt
+│   └── wikilinks.txt
+├── node_modules/...
+├── public/...
+└── src/
+├── middleware.js
+├── app/
+│   ├── layout.tsx
+│   ├── page.module.css
+│   ├── page.tsx
+│   └── registers/
+│       ├── page.tsx
+│       ├── RegisterBrowser.tsx
+│       ├── RegisterDetail.tsx
+│       └── [hex]/
+│           └── page.tsx
+├── components/
+│   ├── Navbar.tsx
+│   └── ThemeDropdown.tsx
+├── scss/
+│   ├── _bootswatch.scss
+│   ├── _explorer.scss
+│   ├── _variables.scss
+│   └── nbn.scss
+├── services/
+│   └── register.service.ts
+└── utils/
+├── register_parser.ts
+└── register_parsers/
+├── reg_default.ts
+└── reg_f0.ts
+```
+- **`data/`**: Contains the raw input data for the Spectrum Next explorer.
+  - `nextreg.txt`: Main register definition file.
+  - `custom_parsers.txt`, `wikilinks.txt`: Auxiliary configuration/data used by the parser.
+- **`src/app/`**: Next.js App Router entrypoint.
+  - `layout.tsx`: Root layout for all routes.
+  - `page.tsx`: Application home page.
+  - `registers/`: Routes and components for the register explorer.
+    - `page.tsx`: Server Component that loads and lists all registers.
+    - `RegisterBrowser.tsx`: Client Component implementing search/filter and listing.
+    - `RegisterDetail.tsx`: Client Component that renders a single register’s details, including modes, notes, and source modal.
+    - `[hex]/page.tsx`: Dynamic route that renders details for a specific register by hex address.
+- **`src/components/`**: Shared UI components such as `Navbar` and `ThemeDropdown`.
+- **`src/services/register.service.ts`**: Service layer responsible for loading and caching parsed register data.
+- **`src/utils/register_parser.ts` & `src/utils/register_parsers/`**: Parsing logic for `nextreg.txt`, including mode/bitfield handling and any register-specific parsing extensions.
+
+## Implementation Details
+
+Comment what the code does, not what the agent has done. The documentation's purpose is the state of the application today, not a log of actions taken.
+
+### Data Parsing
+
+- `getRegisters()` in `src/services/register.service.ts`:
+  - Reads `data/nextreg.txt` from disk.
+  - Uses `parseNextReg()` from `src/utils/register_parser.ts` to convert the raw text into an array of `Register` objects.
+  - Returns the in-memory representation of all registers (and can be extended to cache results across calls).
+
+- `parseNextReg()` and related helpers in `register_parser.ts`:
+  - Parse the custom `nextreg.txt` format into structured data:
+    - Register addresses (hex/dec).
+    - Names, notes, and descriptive text.
+    - Per-mode read/write/common bitfield views.
+    - Optional source lines and external links (e.g. wiki URLs).
+  - Delegate special-case parsing to functions in `src/utils/register_parsers/` (e.g. `reg_default.ts`, `reg_f0.ts`) when needed.
+
+### React / Next.js Patterns
+
+- **Server Components**:
+  - `src/app/registers/page.tsx` and `src/app/registers/[hex]/page.tsx` are Server Components.
+  - They call `getRegisters()` on the server and pass the resulting data down to client components as props.
+
+- **Client Components**:
+  - `RegisterBrowser.tsx`:
+    - Marked with `'use client'`.
+    - Uses React state to manage search input and filtered results.
+    - Renders a list or grid of registers.
+  - `RegisterDetail.tsx`:
+    - Marked with `'use client'`.
+    - Renders a single register with tabs for different access modes.
+    - Uses a modal to show the original source lines for the register.
+
+- **Dynamic Routing**:
+  - `src/app/registers/[hex]/page.tsx`:
+    - Resolves the `[hex]` URL segment.
+    - Looks up the corresponding register by `hex_address`.
+    - Calls `notFound()` when no matching register exists.
+
+### Working Patterns***
+
+- git branching:
+  - Do not create new branches
+- git commits:
+  - Do not commit code - just create COMMIT_EDITMSG file for manual commiting.
+- git commit messages:
+  - Use imperative mood (e.g., "Add feature X", "Fix bug Y").
+  - Include relevant issue numbers if applicable.
+  - Sign-off commit message as Junie@<hostname>