feat: add markdown renderer and code block highlighting (#50)

### Explanation

_No response_

### Issue

Closes #33 Closes #31

### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

### Documentation

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### Versioning

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Reviewed-on: #50
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/app.css

@@ -6,6 +6,7 @@
   --bg-secondary: #16213e;
   --bg-terminal: #0f0f1a;
   --bg-hover: #2a2a4a;
+  --bg-code: #1e1e2e;
   --accent-primary: #e94560;
   --accent-secondary: #ff6b9d;
   --text-primary: #ffffff;
@@ -18,6 +19,16 @@
   --terminal-tool: #c084fc;
   --terminal-tool-name: #ddd6fe;
   --terminal-error: #f87171;
+
+  /* Syntax highlighting colors (dark) */
+  --hljs-keyword: #f472b6;
+  --hljs-string: #a3e635;
+  --hljs-number: #fbbf24;
+  --hljs-comment: #6b7280;
+  --hljs-function: #c084fc;
+  --hljs-type: #22d3ee;
+  --hljs-variable: #fb923c;
+  --hljs-meta: #94a3b8;
 }
 
 [data-theme="light"] {
@@ -25,6 +36,7 @@
   --bg-secondary: #ffffff;
   --bg-terminal: #f1f3f4;
   --bg-hover: #e8e8e8;
+  --bg-code: #f5f5f5;
   --accent-primary: #e94560;
   --accent-secondary: #ff6b9d;
   --text-primary: #1a1a2e;
@@ -37,6 +49,16 @@
   --terminal-tool: #7c3aed;
   --terminal-tool-name: #8b5cf6;
   --terminal-error: #dc2626;
+
+  /* Syntax highlighting colors (light) */
+  --hljs-keyword: #d946ef;
+  --hljs-string: #16a34a;
+  --hljs-number: #d97706;
+  --hljs-comment: #9ca3af;
+  --hljs-function: #7c3aed;
+  --hljs-type: #0891b2;
+  --hljs-variable: #ea580c;
+  --hljs-meta: #64748b;
 }
 
 html,