chore: remove all deprecated code, backward-compat aliases, and legacy shims

[pyramation]

Summary

Removes all deprecated code, backward-compatibility aliases, type shims, and legacy interfaces across the monorepo. The build passes with these deletions.

Deleted exports/symbols:

• writeSqitchFiles, writeSqitchPlan (aliases for writePgpmFiles/writePgpmPlan)
• SqitchRow type alias (for PgpmRow)
• PgTextClientContext type alias (typo fix alias for PgTestClientContext)
• CustomInflectorPlugin, CustomInflectorPreset (aliases for InflektPlugin/InflektPreset)
• LegacyGraphileOptions interface + graphile field from GetConnectionsInput
• IntrospectionSchema type alias from codegen (alias for QueryIntrospectionSchema)
• codegen/src/core/query-builder.ts re-export shim file (deleted entirely)
• Deprecated NodeTypeRegistryPreset section from README

Other changes:

• Moved toCamelCasePlural/toOrderByTypeName exports from select.ts re-export to canonical naming-helpers source in generators/index.ts
• Removed input.graphile legacy options forwarding from playwright-test
• Removed --template-path deprecation comments from CLI (alias itself still registered)
• Cleaned up "backward compat" phrasing from comments across ~10 files

Review & Testing Checklist for Human

• External consumers of removed symbols: Grep any downstream repos/apps that import CustomInflectorPlugin, CustomInflectorPreset, LegacyGraphileOptions, SqitchRow, writeSqitchFiles, writeSqitchPlan, PgTextClientContext, or IntrospectionSchema. The monorepo build passes, but external consumers will break silently at their next build.
• --template-path CLI alias inconsistency: The deprecation comment was removed from pgpm/cli/src/index.ts but the alias 'template-path': 'template' is still registered on line 37. Decide whether to remove the alias entirely (breaking) or keep it as a silent alias.
• graphile field removal from playwright-test: Verify no existing Playwright test suites pass legacy graphile options via GetConnectionsInput. The input.graphile spread was removed from get-connections.ts:60.
• Run the test suite (pnpm test or targeted package tests) — only pnpm build was verified, not tests.

Notes

• The convertFromMetaSchema/validateMetaObject direct exports from graphql/query were initially removed as "backward-compat" but had to be restored because graphql/codegen imports them directly. They are part of the active public API, not legacy shims.

Link to Devin session: https://app.devin.ai/sessions/9d1d1d33bd734370af00f8c60d72316b
Requested by: @pyramation

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