Implement Phase 1 tasks 1.5-1.7 + 1.9 (Codec 8/8E/16 parsers + fixture suite)

- Codec 8 parser (1-byte IO IDs, no NX/Generation Type)
- Codec 8 Extended parser (2-byte IO IDs + variable-length NX section)
- Codec 16 parser (mixed widths + Generation Type, supports IO IDs > 255)
- Shared GPS element / timestamp helpers in gps-element.ts
- Fixture loader with bigint/Buffer sentinel encoding and auto-discovery
- 12 fixture pairs across codec8/8E/16 (canonical doc + synthetic edge cases)
- Cross-checked Codec 8 against Traccar's TeltonikaProtocolDecoder (no discrepancies)

26 new tests. Total 62 passing across 10 test files.
typecheck/lint/test/build all clean.

test/fixtures/teltonika/README.md

@@ -0,0 +1,79 @@
+# Teltonika Fixture Suite
+
+Binary protocol fixtures for the Codec 8, 8E, and 16 parsers.
+
+## File format
+
+Each fixture is a pair:
+
+| File | Purpose |
+|------|---------|
+| `<name>.hex` | Hex-encoded AVL body (CodecID + N1 + records + N2) |
+| `<name>.expected.json` | Expected `Position[]` output and ACK record count |
+
+### .hex format
+
+The body slice only — **not** the full TCP packet (no preamble, no DataFieldLength, no CRC).
+This is exactly what `frame.payload` contains and what `handler.handle(body, ctx)` receives.
+
+Whitespace and newlines are stripped before parsing, so you can write multi-line hex for readability.
+
+### .expected.json format
+
+```json
+{
+  "positions": [
+    {
+      "device_id": "FIXTURE",
+      "timestamp": "2019-06-10T10:04:46.000Z",
+      "latitude": 0,
+      "longitude": 0,
+      "altitude": 0,
+      "angle": 0,
+      "speed": 0,
+      "satellites": 0,
+      "priority": 1,
+      "attributes": {
+        "21": 3,
+        "78": "__bigint:0",
+        "100": "__buffer_b64:AAEC"
+      }
+    }
+  ],
+  "ack_record_count": 1
+}
+```
+
+`device_id` is always `"FIXTURE"` — the IMEI comes from the session context, not the body.
+
+#### Attribute value sentinels
+
+| Sentinel | Decoded type | Example |
+|---------|-------------|---------|
+| number literal | `number` | `24079` |
+| `"__bigint:<decimal>"` | `bigint` | `"__bigint:893700218"` |
+| `"__buffer_b64:<base64>"` | `Buffer` | `"__buffer_b64:qw=="` |
+
+For a zero-length Buffer, use `"__buffer_b64:"` (empty base64 string).
+
+## How to add a new fixture
+
+1. Get the AVL body bytes (from a live capture, a device emulator, or hand-computed).
+2. Write the body as hex into `<name>.hex`.
+3. Manually trace the expected parse output and write `<name>.expected.json`.
+4. Run `pnpm test` — the new fixture is automatically discovered and tested.
+
+No changes to any test file are needed.
+
+## Bootstrap vs. synthetic fixtures
+
+- **Bootstrap** fixtures (01-canonical, etc.) are sourced directly from the Teltonika documentation hex examples. Their expected outputs are read from the doc's parsed tables.
+- **Synthetic** fixtures are hand-constructed for edge cases not covered by the canonical examples. Their expected outputs are computed manually and cross-checked.
+
+## Cross-check methodology
+
+Synthetic Codec 8 fixtures were cross-checked against the Traccar open-source
+decoder (`TeltonikaProtocolDecoder.java`) for field widths and IO section parsing.
+No discrepancies were found for the basic N1/N2/N4/N8 sections.
+The NX section in Codec 8E has no equivalent in older Traccar versions; it was
+verified by byte-level manual trace only.