Add sequence diagrams to Zephyr Threads & Kernel Events lecture and lab

[Copilot]

Adds PlantUML sequence diagram coverage to the threads/events lecture slides and requires students to produce one in the lab to document ISR→kernel event→thread communication flows.

Lecture (slides/zephyr-threads-events.qmd)

• New slide: "Sequence Diagrams for Thread Communication" — introduces sequence diagrams as a tool for documenting inter-thread/ISR/kernel-service interactions, lists typical Zephyr participants.
• New slide: "PlantUML Sequence Diagram Example" — concrete example showing a button ISR posting BUTTON_EVENT, the kernel event bit array unblocking a worker thread from k_event_wait(), and the thread processing the event:

@startuml
participant "Button ISR\nCallback" as ISR
participant "Kernel Event\nBit Array" as KEvents
participant "Worker Thread" as Worker

Worker -> KEvents : k_event_wait()\n[blocking]
activate Worker #LightBlue

note over ISR : Button Pressed
ISR -> KEvents : k_event_post(BUTTON_EVENT)
KEvents --> Worker : BUTTON_EVENT received
deactivate Worker

Worker -> Worker : process event\n(e.g., change state)
@enduml

• Added PlantUML sequence diagram reference to the Resources slide.

Lab (labs/zephyr-threads-events-lab.qmd)

• New section: "Create a Sequence Diagram" — placed within the kernel_events_refactor work, requiring students to diagram the button ISR → button_events bit array → state machine thread interaction and commit both the .puml source and rendered image under docs/.

Original prompt

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This section details on the original issue you should resolve

<issue_title>add sequence diagrams</issue_title>
<issue_description></issue_description>

<agent_instructions>Add context for how to use sequence diagrams to communicate between threads into https://github.com/mlp6/Embedded-Medical-Devices/blob/main/slides/zephyr-threads-events.qmd. Then ask the students to create a sequence diagram in the lab handout, in addition to the state diagram. Please do all of this development on a dedicated branch.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@mlp6 Add this to the: * [threads lecture](https://github.com/mlp6/Embedded-Medical-Devices/blob/main/slides/zephyr-threads-events.qmd), and * [threads lab](https://github.com/mlp6/Embedded-Medical-Devices/blob/main/labs/zephyr-threads-events-lab.qmd). @mlp6 https://plantuml.com/sequence-diagram

• Fixes add sequence diagrams #5

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