Revise ON/QC scopes proposal: clean-up step, MeshMapper zones, Rigaud bridge

[MrAlders0n]

Follow-up to #97 based on review feedback.

• Clarify that each repeater carries one code per level
• Explain the DM example is onqc because it is the phone default, with a link to the explanation
• Replace the "neutral" point with "easy to split later"
• Drop the nested region def comparison and keep the flat result only
• Move old-region clean-up to step 1 of repeater setup, with a worked example
• City code = your MeshMapper zone; add the region def pattern
• Add a Rigaud bridge example (yul + yow)
• Update zone examples: Renfrew and Calabogie in yow, Trois-Rivières and Rigaud in yul

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