[docs] Refactor "decoders" section to "integrations"

[amotl]

• Wrap previous "decoders" section into toplevel "integrations".
• Improve layout of corresponding "integrations" overview page.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (01d8d24) 53.40% compared to head (1d166b8) 53.40%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #145 +/- ## ======================================= Coverage 53.40% 53.40% ======================================= Files 101 101 Lines 5307 5307 ======================================= Hits 2834 2834 Misses 2473 2473 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `53.40% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=daq-tools#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/daq-tools/kotori/pull/145?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=daq-tools) | Coverage Δ | | |---|---|---| | [kotori/daq/decoder/airrohr.py](https://app.codecov.io/gh/daq-tools/kotori/pull/145?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=daq-tools#diff-a290b3JpL2RhcS9kZWNvZGVyL2FpcnJvaHIucHk=) | `100.00% <ø> (ø)` | | | [kotori/daq/decoder/tasmota.py](https://app.codecov.io/gh/daq-tools/kotori/pull/145?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=daq-tools#diff-a290b3JpL2RhcS9kZWNvZGVyL3Rhc21vdGEucHk=) | `100.00% <ø> (ø)` | | | [kotori/daq/decoder/tts\_ttn.py](https://app.codecov.io/gh/daq-tools/kotori/pull/145?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=daq-tools#diff-a290b3JpL2RhcS9kZWNvZGVyL3R0c190dG4ucHk=) | `89.47% <ø> (ø)` | |

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