[PR] fix: correct table column alignment and non-millisecond timestamp formatting [tsfile-viewer]

["CritasWang (via GitHub)" <gi...@apache.org>]

CritasWang opened a new pull request, #27:
URL: https://github.com/apache/tsfile-viewer/pull/27

   ## Summary
   
   Fixes two defects in the Data Preview of table-model TsFiles, plus a related `atob` regression.
   
   ### 1. Header/body column misalignment
   On table-model files, `measurements` also contains the tag columns (e.g. `plant`, `device`). The fixed **device** column used `key`/`dataIndex = "device"`, colliding with a tag column also named `device`. Since antdv `Table` distinguishes columns by `key`, the header desynced from the body, and `flatRow.device` was overwritten by the measurement value.
   
   **Fix**: the fixed identity column now uses a reserved key `__device__`, fully isolated from tag columns. Tree-model files are unaffected.
   
   ### 2. Timestamps rendered as `NaN-NaN-NaN NaN:NaN:NaN.NaN`
   Source timestamps can be nanoseconds (19 digits, e.g. `1692611833503000000`), which overflow JS `Date` → `Invalid Date` → `NaN`.
   
   **Fix**:
   - Added `normalizeToMs()` (in `utils/timestamp.ts`) to auto-scale seconds / milliseconds / microseconds / nanoseconds to milliseconds.
   - Display stays at millisecond precision. The **exact** original value is preserved without a backend change via a scoped `transformResponse` hook that captures the raw timestamp digit string **before** `JSON.parse` (avoiding lossy `double` conversion), exposed on hover, with an info banner explaining the behavior.
   - CSV export timestamps now use `normalizeToMs` too.
   
   ### 3. `atob` regression fix
   After fileIds became URL-safe base64, `atob()` failed on `-`/`_` characters (and never handled UTF-8 for non-ASCII paths). Extracted `encodeFileId`/`decodeFileId` into `utils/fileId.ts` and replaced all six call sites (file tree, data-preview, chart, metadata).
   
   ## Testing
   - `pnpm build` (vue-tsc + vite) passes.
   - Verified end-to-end in the browser on a real nanosecond table-model file: columns align, timestamp displays as `2023-08-21 17:57:13.503`, hover shows the exact raw value, and sub-millisecond precision is preserved losslessly (raw string `...123456` kept exact, vs `...123500` under naive `String(double)`).
   
   ## Notes
   `timestampRaw` is currently preserved only on the data-preview endpoint. The chart endpoint could get the same treatment if full nanosecond fidelity is needed there.


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