docs(e2e): update READMEs for the consolidated suite layout

[spalladino]

Updates every README in the e2e test section to describe the suite as it will look once the nine open
round-2 consolidation PRs land. This is docs-only — no code, config, or bootstrap.sh changes.

What changed per README

• end-to-end/README.md (root): repointed the LOG_LEVEL example off the deleted
  proving/empty_blocks.test.ts to proving/default_node.test.ts; linked the new p2p README from the
  category table (the p2p row now reads "yes" and points at src/p2p/README.md); and renamed the
  setupBlockProducer submission-window literal 1024 to the named constant NO_REORG_SUBMISSION_EPOCHS.
• end-to-end/src/single-node/README.md: rewrote the cross-chain/ row for the merged layout
  (CrossChainMessagingTest + message_test_helpers.ts, and the l1_to_l2 / l1_to_l2_inbox_drift /
  l2_to_l1 / token_bridge files); folded public_payments/sponsored_payments into
  private_payments.parallel and fixed the stale failures.parallel name to failures; replaced
  slasher_config/sequencer_config with the merged runtime_config; replaced
  world_state_pruning/empty_blocks with the merged default_node; added the previously-missing
  snapshot_sync to the sync/ row; and applied the NO_REORG_SUBMISSION_EPOCHS rename.
• end-to-end/src/multi-node/README.md: named equivocation_offenses in the slashing row (in place
  of the separate duplicate_proposal/duplicate_attestation files) and applied the
  NO_REORG_SUBMISSION_EPOCHS rename in the MOCK_GOSSIP_MULTI_VALIDATOR_OPTS preset.
• end-to-end/src/p2p/README.md (new): created with the content added by test(e2e): extract p2p gossip scenario skeleton and add category README #24500.
• end-to-end/src/automine/README.md and end-to-end/src/infra/README.md: untouched — both are
  behavior-level (no file names) or cover a directory none of the nine PRs change, so they remain accurate
  as-landed.

Assumptions and merge order

• This PR describes the suite assuming the nine open round-2 PRs land: test(e2e): consolidate automine token suites #24489, test(e2e): consolidate automine contracts and effects suites #24490, test(e2e): consolidate cross-chain bridge and messaging suites #24491, test(e2e): merge single-node fee, proving, and sequencer config suites #24492,
  test(e2e): name shared timing presets and collapse proof-submission constants #24494, test(e2e): unify slashing timing profiles and merge duplicate suites #24495, test(e2e): dedupe multi-node block-production and governance test setups #24498, test(e2e): extract p2p gossip scenario skeleton and add category README #24500, test(e2e): split node-killing HA test into its own composed suite file #24503. The layout it documents is the union of the current base branch
  and all nine diffs.
• Where one of those PRs already edits or adds a README, the overlapping hunk is taken verbatim from its
  branch, so this PR and the other one merge cleanly in either order: the new p2p README is test(e2e): extract p2p gossip scenario skeleton and add category README #24500's file
  as-is, and the multi-node slashing row already matches the base branch (the "name both inactivity files"
  fix from test(e2e): unify slashing timing profiles and merge duplicate suites #24495 has already propagated to merge-train/spartan-v5).