docs: add CHANGELOG.md with 1.0.0 release notes

Add comprehensive CHANGELOG.md documenting the initial 1.0.0 release
with all features, supported formats, and standards compliance.

Also includes a changeset for the next patch release to ensure the
CHANGELOG is included in the published package.

Author: lxcid

.changeset/add-a-changelog.md

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+---
+"@taskade/temporal-parser": patch
+---
+
+docs: add CHANGELOG.md with 1.0.0 release notes

CHANGELOG.md

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+# @taskade/temporal-parser
+
+## 1.0.0
+
+### Major Changes
+
+- Initial release of temporal parser with comprehensive ISO 8601, RFC 3339, and IXDTF support
+
+  **Features:**
+  - Lexer-based tokenization for temporal strings
+  - Recursive-descent parser with extensible architecture
+  - Support for dates, times, timezones, durations, and ranges
+  - IXDTF annotations and bracket extensions
+  - Zero runtime dependencies
+  - Full TypeScript support with strict mode
+  - 91% test coverage with 271 test cases
+
+  **Supported Formats:**
+  - Dates: `2025`, `2025-01`, `2025-01-12`
+  - Times: `T10:30`, `T10:30:45`, `T10:30:45.123456789`
+  - Timezones: `Z`, `+08:00`, `-05:30`, `[Asia/Singapore]`
+  - Durations: `P1Y2M3D`, `PT4H5M6S`, `P1Y2M3DT4H5M6S`
+  - Ranges: `2025-01-01/2025-12-31`, `/2025-12-31`, `2025-01-01/`
+  - Annotations: `[u-ca=gregory]`, `[!u-ca=iso8601]`
+
+  **Standards Compliance:**
+  - ISO 8601 date/time formats
+  - RFC 3339 timezone semantics (Z vs +00:00 vs -00:00)
+  - IXDTF extensions for calendar and timezone annotations
+  - Correct timezone offset range (UTC-12:00 to UTC+14:00)