feat(config): support repeated --mcp-config flags

[ghul0]

Problem

The adapter only preserved a single --mcp-config value end-to-end even though layered MCP configuration is useful for combining shared and project-specific definitions.

Root Cause

The config loading path still treated --mcp-config as a single string in key wiring points:

• argv parsing only exposed one path
• config loading and provenance tracking expected one override path
• /mcp panel wiring still relied on the stale single-path flow

Fix

• parse repeated --mcp-config flags from argv in order
• let loadMcpConfig() merge multiple config files in order before project-local overrides
• let getServerProvenance() track multiple user config sources
• update initialization and /mcp panel wiring to use getConfigPathsFromArgv() directly so repeated flags survive end-to-end
• keep the existing single-path behavior intact when only one config path is provided

Summary

• add getConfigPathsFromArgv() in utils.ts
• extend config.ts to accept multiple override paths for config loading and provenance
• update index.ts, init.ts, and commands.ts to use the repeated-flag path flow
• add tests for config merging, provenance, argv parsing, and call-site wiring

Testing

Targeted tests for this change

npx vitest run __tests__/config.test.ts __tests__/config-provenance.test.ts __tests__/utils.test.ts __tests__/wiring.test.ts

 RUN  v3.2.4 /tmp/pi-mcp-adapter-pr1

 ✓ __tests__/wiring.test.ts (5 tests) 2ms
 ✓ __tests__/utils.test.ts (10 tests) 3ms
 ✓ __tests__/config-provenance.test.ts (2 tests) 3ms
 ✓ __tests__/config.test.ts (10 tests) 5ms

 Test Files  4 passed (4)
      Tests  27 passed (27)
   Duration  217ms

Maintainer note

upstream/main currently does not track examples/interactive-visualizer/dist/app.html or dist/server.js, so the unrelated __tests__/interactive-visualizer-server.test.ts fails on a full-suite run before this PR's changes are involved.