feat: introduced render_mermaid tool for ASCII diagram output

- Added render_mermaid tool to convert Mermaid diagrams to ASCII output with configurable rendering options.
- Added renderMermaid.enabled setting to control availability of the render_mermaid tool.
- Changed Mermaid rendering from PNG terminal graphics to ASCII text format across theme and TUI components.
- Migrated mermaid utilities from pi-tui to pi-utils package with new ASCII rendering functions.
- Removed PNG-based mermaid rendering APIs (getMermaidImage, renderMermaidToPng) in favor of ASCII alternatives.

package.json

@@ -37,7 +37,8 @@
 		"release": "bun scripts/release.ts",
 		"generate-models": "bun --cwd=packages/ai scripts/generate-models.ts",
 		"generate-docs-index": "bun --cwd=packages/coding-agent run generate-docs-index",
-		"sync-exports": "bun scripts/sync-exports.ts"
+		"sync-exports": "bun scripts/sync-exports.ts",
+		"mermaid-build": "bun scripts/mermaid-build.ts"
 	},
 	"devDependencies": {
 		"@biomejs/biome": "^2",