feat(schema): port schema introspect from Go CLI

[beengud]

Closes #8

Summary

Ports the schema introspect command from the deprecated Go Observe CLI (cmd_schema.go) into the TypeScript CLI.

observe schema introspect [--type <TypeName>]

• Runs a GraphQL introspection query against the Observe /v1/meta endpoint and prints the result as formatted JSON.
• --type <TypeName> filters the output to a single named type (e.g. Dashboard, DashboardInput, Mutation, Query), matching against __schema.types[].name client-side. Mirrors the Go --type filtering exactly, including the type "X" not found error + non-zero exit.
• Gracefully handles the case where introspection is disabled on the tenant: the GraphQL error is detected and reported with a clear message plus exit code 1.

Implementation notes

• This is a raw introspection query, not a codegen'd domain operation, so it does not depend on src/gql/generated/graphql.ts. The introspection query string replicates the exact query the Go CLI used (Schema_Introspect).
• The fetch (src/gql/schema/introspect-schema.ts) mirrors the auth/header approach of executeGraphQL in src/gql/gql-request.ts (same Authorization: Bearer <customerId> <token> header, same observeApiHeaders, same /v1/meta URL and GqlApiError handling) but issues the raw query directly since there is no TypedDocumentNode to print().
• The .graphql file (src/gql/schema/introspect-schema.graphql) is included for parity with the repo convention and is kept in sync with the inline query string.

Files added/changed

Added:

• src/commands/schema/introspect.ts
• src/commands/schema/index.ts
• src/commands/schema/introspect.test.ts
• src/gql/schema/introspect-schema.ts
• src/gql/schema/introspect-schema.graphql

Changed:

• src/app.ts — registered schema route (added before cli, which remains last)
• README.md — added observe schema introspect to the Commands table (order matches src/app.ts)
• AGENTS.md — added schema resource to the Project Structure section (commands + gql)

Verification status

• Codegen / typecheck / full build could NOT run locally: GraphQL introspection is disabled on the available tenant, so bun run codegen cannot run and src/gql/generated/graphql.ts does not exist. This is expected; nothing under src/gql/generated/ was hand-written or committed. Note: this command itself does not import generated types, so it is unaffected by the missing codegen.
• Runtime caveat: because introspection is disabled on the test tenant, this command cannot be runtime-verified here. It is implemented faithfully against the Go source so it will work on tenants where introspection is enabled, and it handles the introspection-disabled error gracefully (clear message + exit 1).
• Unit tests run and passing: bun test src/commands/schema/introspect.test.ts -> 5 pass, 0 fail. Covers: full-schema JSON output, --type filtering to a single type, --type not-found exit-1, introspection-disabled message + exit-1, and generic API error exit-1. Tests mock the introspection fetch module via mock.module(...) before importing the command, so they run cleanly without codegen.

Assumptions / risks

• The introspection query field set (fields, inputFields, enumValues, interfaces, possibleTypes, nested ofType two levels deep, includeDeprecated: true) is copied verbatim from the Go CLI and is standard GraphQL introspection, but could not be validated against a live schema since introspection is disabled.
• Introspection-disabled detection matches GraphQL errors whose message contains "introspection" (case-insensitive). The exact server error wording could not be confirmed on the live tenant; if it differs, the command still exits 1 via the generic API Error path.