chore: remove slide_creator agent and slide generation

[locnguyen1986]

Summary

Removes the slide-creator agent and all slide-specific code across the backend services, web app, tests, and tooling. The other agents (deep_research, doc_generator, pdf_generator, spreadsheet_generator) and generic .pptx file upload are intentionally preserved.

The slide executor was the de-facto handler for all ArtifactCreate steps (doc/pdf/spreadsheet/deep_research all emit store_artifact), so the shared generic path was first extracted into a new planners/artifactexec package before the slide-specific code was deleted.

Changes

response-api

• New internal/domain/agent/planners/artifactexec package — generic ArtifactCreate executor extracted from the slide package.
• Deleted the slide_creator planner/steps, assets/slide_creator + assets/slide_renderer, the slides skill template, and the now-dead RoutingExecutor.
• Rewired DI: deepResearchExecutor for tool/LLM calls, GenericArtifactExecutor for artifact creation.
• Removed ContentTypeSlides, AgentTypeSlideCreator, SkillTypeSlides, SlideCreator* metadata/schemas/examples, SlidesMetadata, MediaArtifact.SlidesImages, RenderSlidesPPTX, the SLIDE_RENDERER_* / SKILL_SLIDES_ENABLED config, and the generate_slide request special-casing.

mcp-tools

• Removed the slide_creator agent-proxy handling and the slide-only generation package.

llm-api

• Dropped the slide_generate MCP tool key.

web

• Removed the slide viewer, the "Presentations" artifact filter, slide rendering in the gallery/card/sidebar, and slide metadata parsing. Presentation file upload is kept.

tests / docs / tooling

• Unit + integration tests, e2e seed SQL, postman collections, env-var docs, .env.template, and the Makefile updated; slide assertions repointed to doc_generator; orphaned test-agent-slide target removed.

Local-docker fixes (separate commit — pre-existing, unrelated to slides)

While verifying the stack in Docker, two pre-existing issues blocked a healthy bring-up and are fixed in d944305:

• media-api: the default local storage backend registered a path-based static mount at /v1/files/*filepath that conflicts with /v1/files/:id and panics gin at startup. Files are served by ID via the Proxy handler, so the redundant static mount is removed.
• web: the container healthcheck used http://localhost:3001 (resolves to IPv6 ::1, where nginx on 0.0.0.0:3001 doesn't answer) → switched to 127.0.0.1.

Verification

• go build ./... (+ -tags wireinject) passes for response-api, llm-api, mcp-tools; web builds (tsc -b && vite build).
• response-api unit tests pass (agent list now returns deep_research/doc_generator, no slide_creator).
• Full stack built and deployed in local Docker — all 9 containers healthy (infra + llm-api, response-api, media-api, mcp-tools, web); /v1/agents route wired, guest-login intact.
• Repo-wide sweep confirms no remaining slide_creator / slide-agent references (animation classes and pptx-upload MIME types intentionally retained).