docs: add CHANGELOG for 1.5.0 release

Author: seflue

CHANGELOG.md

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+# Changelog
+
+## 1.5.0
+
+**Snacks.nvim support**
+
+[snacks.nvim](https://github.com/folke/snacks.nvim) can now be used as picker backend alongside Telescope.
+
+**New features**
+
+- Tag search: `search_tags()` lets you browse and filter by org tags
+- Filter headlines by current file, open buffers, or specific files
+- Picker title shows active filters
+- Location column can show category instead of filename (`location_preference`)
+- Jumping to a headline now sets a jumplist mark (`<C-o>` to go back)
+
+**Fixes**
+
+- Per-call `adapter` option was ignored after first call
+- `get_api_file()` could crash on invalid filenames
+- Pressing `<CR>` on an empty result no longer errors
+
+**Under the hood**
+
+- Restructured codebase for multi-adapter support
+- Added test suite and GitHub Actions CI
+
+**Full Changelog**: https://github.com/nvim-orgmode/telescope-orgmode.nvim/compare/1.4.3...1.5.0