refactor(ENG-277): Extract INIT-MARKET-PDA procedure from REGISTER-MARKET

[alnoki]

Changes

1. Extract market PDA derivation, CPI field population, and
   CreateAccount invoke into a standalone INIT-MARKET-PDA
   procedure (init_market_pda.s), entered and exited via
   ja (no function call overhead, all registers preserved)
2. Reorder REGISTER-MARKET to check System Program and Rent
   sysvar before PDA derivation, consolidating all PDA signer
   seed initialization into the new procedure
3. Move CreateAccount lamports/space calculation into
   INIT-MARKET-PDA (r9 = acct is never clobbered, so the Rent
   sysvar read works inside the procedure)
4. Remove acct field from RegisterMarketFrame and its
   RM_FM_ACCT_OFF constant (r9 survives the entire procedure
   and both syscalls, making the save/restore unnecessary)
5. Add INIT-MARKET-PDA algorithm spec with input, require, and
   ensure annotations documenting register contracts
6. Add "Market PDA initialization" section under Helpers in
   markets.md and register the algorithm in index.json
7. Update test case ordering to match new control flow (PDA
   mismatch tests now follow Rent sysvar tests)
8. Update pda_mismatch_accounts to provide valid System
   Program and Rent sysvar accounts (required now that those
   checks precede PDA derivation)
9. Add // Verifies: INIT-MARKET-PDA comments to all test
   cases that exercise the extracted procedure

[linear]

ENG-277