feat: Overhaul MCP server for 2025-11-25 spec and add llms.txt doc

[jahvon]

Refactors the MCP server to conform to current MCP spec best practices and adds an
llmstxt.org-style docs index so AI clients can pull documentation on demand rather
than having it pre-baked into tool responses.

MCP server

• Upgrade mcp-go v0.43.2 -> v0.47.1
• Declare listChanged on tool/resource capabilities and subscribe on resources
• Add WithOutputSchema on every tool using new Go output structs
• Cursor-based pagination (opaque base64 offsets) on list_workspaces,
  list_executables, get_execution_logs
• Structured error responses with machine-readable codes (INVALID_INPUT,
  NOT_FOUND, EXECUTION_FAILED, CANCELLED, VALIDATION_FAILED, etc.)
• Progress notifications and context cancellation for execute/sync_executables
• New MCP resources: flow://workspace/{name}, flow://executable/{ws}/{ns}/{name},
  flow://flowfile/{path}, flow://logs/{run-id}
• Emit resources/list_changed after switch_workspace, sync_executables, and
  write_flowfile
• New tools: write_flowfile (YAML-validated flowfile authoring) and
  get_workspace_config
• Split tools.go into tools_workspace.go / tools_executable.go / tools_system.go
• Extend CommandExecutor with ExecuteContext for cancellation support

get_info slimdown

• Dropped embedded concepts/file-types markdown and JSON schemas (~20KB)
• Returns compact summary, docsUrl, llmsTxtUrl, schemaUrls, guideUrls instead
• Removed the now-unused MCP resource copies and the docsgen path that produced
  them

Docs

• Add docs/public/llms.txt following the llmstxt.org format
• Add docs/public/robots.txt pointing at the sitemap
• Enable VitePress built-in sitemap generation
• Update server-instructions.md to describe the new get_info shape and point
  agents at llmsTxtUrl / schemaUrls / guideUrls

Tests

• New pagination unit tests (empty, first/middle/last page, invalid cursor,
  cursor past end, round-trip)
• New Ginkgo specs: resource template registration, output schema presence,
  structured error responses, write_flowfile (valid/invalid extension/invalid
  YAML/exists/overwrite), list_executables pagination

[codecov]

Codecov Report

❌ Patch coverage is 58.42349% with 269 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/mcp/resources.go	21.54%	142 Missing ⚠️
internal/mcp/tools_workspace.go	61.06%	40 Missing and 4 partials ⚠️
internal/mcp/tools_executable.go	78.21%	23 Missing and 16 partials ⚠️
internal/mcp/tools_system.go	72.88%	25 Missing and 7 partials ⚠️
internal/mcp/tools.go	46.15%	7 Missing ⚠️
internal/mcp/command_executor.go	0.00%	3 Missing ⚠️
internal/mcp/errors.go	83.33%	1 Missing and 1 partial ⚠️

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