Add use case model, ADR-0001, dictionary update and reviews RC-011 to RC-023

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docs/uc-001/ssd.md

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+# System Sequence Diagram
+
+## Metadata
+| Key | Value |
+| --- | --- |
+| ID | SSD-001 |
+| CrossReference | [UC-001] |
+| Language | en |
+| Domain | it |
+
+## Version History
+| Date | Status | Author | Reviewer | Change | Commit |
+| --- | --- | --- | --- | --- | --- |
+| 2026-10-13 | Accepted | Jens Tirsvad Nielsen | AI as stand-in for S01 | Initial version | pending |
+
+---
+
+## Source Use Case
+
+Count squirrels by fur colour ([UC-001]) — scenario: main success scenario. The alternate flow 1a (census file missing) is the second diagram; flow 2a has no system message of its own.
+
+## Diagram
+
+```plantuml
+@startuml
+actor Participant as A
+participant ":System" as S
+A -> S : countByFurColor(censusFile, summaryFile)
+S --> A : summary
+@enduml
+```
+
+```plantuml
+@startuml
+actor Participant as A
+participant ":System" as S
+A -> S : countByFurColor(censusFile, summaryFile)
+S --> A : censusFileMissing
+@enduml
+```
+
+## System Operations
+
+| Step | Message | Parameters | Return | Use case step |
+| --- | --- | --- | --- | --- |
+| 1 | countByFurColor | censusFile, summaryFile | summary (colour count of each fur colour) | 1 (input), 2 (count), 3 (write), 4 (shown to the participant) |
+| 1a | countByFurColor | censusFile, summaryFile | censusFileMissing | 1a |
+
+Steps 2 to 4 of the use case are the work of the system inside one operation: the system receives one message and returns one result, so one message covers steps 1 to 4.
+
+## Lifecycle Notes
+
+The system instance lives for one run of the program; nothing is kept between runs.
+
+---
+
+[UC-001]: ./uc.md