fix: prepare truthful v0.4.1 correction release (COD-445)

[shivros]

Summary

Truthful follow-up correction release for layered context sources. The published immutable v0.4.0 tag stays untouched; it shipped the feature but its CLI and MCP implementation metadata incorrectly reported 0.3.0.

This PR prepares v0.4.1 by:

• updating CLI and MCP version constants to 0.4.1;
• updating the pinned README install command;
• documenting the immutable v0.4.0 packaging defect and corrective release in the changelog.

Verification

go generate ./...
go build ./...
go test -race -count=1 ./...
go vet ./...
gofmt -l .  # empty
go run . --version  # creed 0.4.1
git diff --check

All passed. scripts/check-generated.sh intentionally requires a clean tree before it runs go generate; after generation, the only changed files were the four intended source/docs files.

Release follow-up

After this PR merges, publish an immutable v0.4.1 tag/release and verify a clean-cache go install github.com/techgodhq/creed@v0.4.1 reports creed 0.4.1. Do not move or rewrite v0.4.0.

Closes COD-445.

[shivros]

🤖 Automated Review Panel

GPT-5.6-terra (openai-codex)

APPROVE — the correction keeps immutable v0.4.0 intact, updates both user-visible version constants to 0.4.1, updates the install documentation, and accurately documents the correction. No concrete correctness or goal-alignment issues found.

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GPT-5.5 (openai/gpt-5.5)

APPROVE — the supplied diff aligns with the release-correction goal: it leaves v0.4.0 untouched, fixes CLI and MCP metadata, updates the pinned install command, and records the correction in the changelog. No blockers found.

[shivros]

Auto-Merge Gate

Confidence: 0.96

The narrowly scoped v0.4.1 correction aligns with COD-445’s explicitly authorized immutable-release remediation: it preserves v0.4.0, corrects both CLI and MCP version metadata, updates the pinned install command, and documents the defect accurately. CI passed: Test, Lint, and Secret Scan. The on-PR dual-model review panel found no unresolved correctness issues.

Scope limit: this merge does not publish the v0.4.1 tag/release or complete the clean-cache install verification; those remaining acceptance items stay tracked in COD-445.