docs(asset-leasing): replace em-dashes with regular dashes; say 'token A' not 'mint A'

- Replaced all 74 em-dashes (\u2014) with regular dashes (-) per Mike's
  preference. Em-dashes are LLM-output tells; regular dashes
  everywhere.
- Section 1 introduced the two assets as 'mint A' and 'mint B',
  conflating the asset itself with the mint account that controls
  its supply. The asset is a token; the mint is the factory. Now
  reads 'token A' / 'token B' for the asset, with 'leased mint' /
  'collateral mint' kept ONLY where the prose is genuinely talking
  about the mint account (token-account field descriptions,
  instruction-handler walkthroughs - these correctly refer to the
  mint of an associated token account).

Note: the old per-instruction tables in section 2 still use markdown
tables. Those are a separate cleanup; flagged for follow-up.

Author: Edward (OpenClaw)