chore: release v1.5.0

[tongsh6]

Summary

• Bump version from 1.4.0 to 1.5.0
• Add CHANGELOG.md with full release history (v1.2.0 ~ v1.5.0)

v1.5.0 Highlights

• Config validation: validateConfig() with shared types and defaults
• Performance: In-memory budget tracker (no per-message file reads)
• Model pricing: claude-opus-4.6, gemini-2.0-flash-lite, corrected Gemini prices
• Quality: 31 unit tests, GitHub Actions CI (Node 18 + 22)
• Refactor: Shared module lib/shared.ts consolidates all types and utils

[Copilot]

Pull request overview

Release-prep PR to publish v1.5.0 of opencode-token-tracker, adding a changelog and updating the package version.

Changes:

• Bump package.json version from 1.4.0 to 1.5.0.
• Add CHANGELOG.md with release notes/history from v1.2.0 through v1.5.0.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
package.json	Updates published package version to 1.5.0.
CHANGELOG.md	Adds a Keep-a-Changelog formatted release history and v1.5.0 notes.

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[Copilot]

package.json version is bumped to 1.5.0, but package-lock.json still records the root package version as 1.0.0 (both top-level and packages[""]). For release consistency (and to avoid confusing downstream tooling), regenerate/update the lockfile so its root version matches the package version.