docs: dynamically render Mermaid diagrams on GitHub Pages

[lostcontrol]

This PR fixes the rendering of Mermaid diagrams on GitHub Pages. Since standard GitHub Pages restrict the use of third-party Jekyll plugins to render Mermaid diagrams during the build phase, this introduces a lightweight client-side solution.

The implementation relies on the fact that standard jekyll-theme-leap-day allows injecting custom HTML headers via docs/_includes/head-custom.html. It dynamically loads the Mermaid ESM module via a CDN, detects Jekyll-generated .language-mermaid code blocks, properly unescapes the code snippet, and then instructs Mermaid to render them on the fly. This keeps the markdown clean and standard, requiring zero dependencies or manual .mermaid tag wrapping.

---

PR created automatically by Jules for task 14570960433883998734 started by @lostcontrol

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
controller
actor.py	61	10	84%	41–42, 63, 74, 80–84, 104
arduino.py	44	44	0%	18–81
config.py	11	1	91%	32
device.py	288	164	43%	44, 47, 50, 53, 56–57, 64–65, 68–69, 72, 78, 81, 91, 95, 117–122, 125, 128, 131–134, 145–147, 177, 182, 189–192, 195–196, 201–220, 225–228, 232–244, 249–259, 262–264, 269–270, 273–291, 296–302, 305–307, 311–312, 315, 318, 321, 326–327, 332, 335–364, 367–390, 395–398, 401, 405
disinfection.py	158	84	47%	48–52, 64, 66, 87–88, 95–98, 101–102, 119–145, 148–149, 152–153, 156–157, 160–161, 165–166, 169–170, 173, 176–184, 187–189, 192–196, 199–215, 218–220
dispatcher.py	38	38	0%	18–329
filtration.py	612	423	31%	74, 82–84, 94, 97, 100, 106, 118–120, 129, 132, 140–145, 148–153, 156–161, 164–168, 171–174, 177, 180–189, 221–309, 312–315, 318–323, 326–328, 331–332, 335–336, 339–341, 344, 347, 350–352, 355–356, 359–364, 367–372, 375–380, 383–387, 390–391, 394–395, 398–402, 405–406, 409–411, 414–416, 419–421, 424–425, 428, 431, 434–440, 443, 446, 449–451, 454–461, 464–477, 480–481, 485–493, 496–507, 510–514, 518–526, 529–537, 540–544, 547–552, 555–564, 568–572, 575–587, 591–599, 602–607, 610, 614–618, 621–624, 627–630, 633–634, 639, 642, 645, 649–653, 656–666, 669–670, 673–679, 683–693, 696–698, 701–707, 710, 714–720, 723–727, 730–734, 737–738, 741–743, 746–751, 755–768, 771–772, 775–776, 779–781, 784–792, 795–798, 801–804, 807–812, 816–818, 821–826, 829–832, 835–837
heating.py	188	188	0%	18–269
lcd.py	55	9	84%	36–44
light.py	22	22	0%	18–50
mqtt.py	47	47	0%	18–78
sensor.py	99	42	58%	33, 42, 51, 55, 58–61, 69–70, 73, 76, 79–80, 87–89, 92–98, 110, 113, 127–128, 135–137, 140–152
swim.py	82	25	70%	63–64, 77–78, 87–89, 92–97, 110–112, 115–120, 123–126
tank.py	110	110	0%	18–163
TOTAL	1899	1207	36%

Tests	Skipped	Failures	Errors	Time
99	0 💤	0 ❌	0 🔥	19.354s ⏱️