chore: remove ir release module and update doc

[tianzhou]

No description provided.

[Copilot]

Pull Request Overview

This PR removes the standalone IR package release infrastructure, consolidating the IR package as an internal component of the main pgschema project rather than a separately versioned Go module.

Key changes:

• Removed IR package release workflow and version management
• Eliminated IR integration tests that validated SQL parsing vs database inspection equivalence
• Updated documentation to reflect inspector-only approach

Reviewed Changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/dump/README.md	Removed documentation about IR integration tests
ir/ir_integration_test.go	Deleted entire integration test suite (673 lines)
ir/go.mod	Removed separate go.mod for IR package
ir/VERSION	Removed IR version file
ir/README.md	Updated to reflect inspector-only usage and removed parsing/versioning sections
go.mod	Consolidated IR as internal package, moved dependencies to main level
CLAUDE.md	Updated architecture notes to reflect IR as internal package
.github/workflows/release-ir.yml	Removed IR package release workflow

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