docs(contract): record Phase 0 OTF revision

[kars85]

Why

Completes the OTF/Firmware revision-record step in OpenSprinkler-App#11 without changing either dependency path.

What

• distinguish OTF library ESP32 capability from OpenSprinkler-Firmware's actual ESP8266, OSPi/Linux, and DEMO targets
• document the current split dependency model:
  • ESP8266: mutable upstream PlatformIO constraint ^0.2.0
  • DEMO/Linux: upstream gitlink 4e93061538da197e1820c7b325a3c996ff7851ea
• record 75fe760187ac932e56876e1954540089686d6082 as the intended kars85 fork review candidate
• preserve the Phase 4 gate: ESP8266 and DEMO must build against the same exact revision before either dependency moves
• refresh drifted Firmware source citations

Validation

• candidate SHA matches current origin/master as of 2026-07-16
• library.json remains version 0.2.1
• git diff --check
• same-revision ESP8266 + DEMO builds (required before dependency changes; no dependency change is in this PR)

Safety

Documentation only. No dependency, protocol, cloud transport, or hardware change.

[gemini-code-assist]

Code Review

This pull request updates ARCHITECTURE.md to clarify supported firmware targets (specifically highlighting ESP8266 and Linux/DEMO while noting ESP32 is a library capability), details dependency wiring and specific Git commit revisions, and updates line number references to match the current codebase. The feedback suggests a minor improvement to use lowercase "firmware" instead of capitalized "Firmware" in the newly added text for consistency.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

For consistency with the rest of the document where "firmware" is lowercase when referring to the software, consider using lowercase "firmware" here instead of capitalized "Firmware".

Suggested change

	dependency. Before the Firmware changes its PlatformIO constraint or native gitlink,
	dependency. Before the firmware changes its PlatformIO constraint or native gitlink,