fix: resolve MCP sidecar image failures (issue #40)

Three fixes for broken MCP sidecars:

1. Remove GitHub MCP sidecar entirely - the upstream image
   (ghcr.io/modelcontextprotocol/servers/github) is discontinued.
   GitHub MCP is now accessed via Copilot API instead.

2. Fix Playwright MCP image - changed from non-existent
   microsoft/playwright-mcp to mcr.microsoft.com/playwright/mcp
   (the official Microsoft Container Registry image).

3. Fix pgtuner MCP startup command - changed --transport to --mode
   and added --host 0.0.0.0 to match the current pgtuner_mcp CLI.

Bumps chart version to 0.3.3.

Closes #40

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Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

chart/values.schema.json

@@ -177,9 +177,6 @@
             "homeassistant": {
               "$ref": "#/$defs/mcpSidecar"
             },
-            "github": {
-              "$ref": "#/$defs/mcpSidecar"
-            },
             "pgtuner": {
               "$ref": "#/$defs/mcpSidecar"
             },