JSON schemas for apic.yaml, http-client.env.json and .apic/session.json #64

Why

apic.yaml has grown keys (env, dir, timeout, maxBodyBytes, auth.default, auth.allowExec, test.paths, and more coming: cookies, tls, proxy, retry, history). Nothing validates it or offers completion. Published JSON schemas give every editor completion and validation for free through the YAML and JSON language servers, and the VS Code extension registers them directly. Docs can render the config reference from the same source.

What

• Generate docs/schemas/apic.schema.json, http-client.env.schema.json and session.schema.json from the Go structs (internal/project/project.go config types, internal/env) with task schemas, using struct tags for descriptions so the docs and the schema share one source. The MCP SDK already pulls in google/jsonschema-go; use it or invopop/jsonschema in a scripts/schemas program (not part of the binary).
• Publish them on the docs site at stable URLs (https://datagriff.github.io/api-caller/schemas/apic.schema.json) and add them to SchemaStore (schemastore/schemastore PR) so editors pick them up by filename.
• apic init writes # yaml-language-server: $schema=… as the first line of apic.yaml.
• CI fails if the committed schemas are stale (task schemas && git diff --exit-code).
• docs/cli.md "Configuration file" section is generated from the schema descriptions.

Where

scripts/schemas/main.go, Taskfile.yml, .github/workflows/ci.yml, docs/schemas/, mkdocs.yml (ensure the JSON files are copied), internal/cli/init.go, docs/cli.md.

Tests

The generator's output validates the example projects' files and the demo project; a negative test with a misspelled key fails validation.