docs(run-a-node): fix historical proofs ExEx setup and compose PROFILE default

[kriss39]

What changed? Why?

Three statements on specifications/node-operators/run-a-node don't match what base/base actually does (checked against main at 9469da2):

1. RETH_HISTORICAL_PROOFS=true alone does nothing. etc/scripts/node/execution-entrypoint only adds --proofs-history (and runs proofs init) when RETH_HISTORICAL_PROOFS == "true" and RETH_HISTORICAL_PROOFS_STORAGE_PATH is non-empty. There is no <datadir>/proofs default; an operator following the page as written gets a node with the ExEx silently disabled. The page now shows both variables, with /data/proofs as the example path (the execution container's data dir).
2. Default retention is 30 days, not 28. crates/execution/node/src/args.rs: DEFAULT_PROOFS_HISTORY_WINDOW_BLOCKS = 1_296_000 (30 * 24 * 60 * 60 / 2).
3. RETH_PROOFS_HISTORY_WINDOW does not exist. No file in base/base reads it; the window is the --proofs-history.window CLI flag, and the entrypoint doesn't map an env var to it. The note now says that instead of promising an env var that is ignored.

Separately, the compose variable table listed PROFILE as defaulting to maxperf. docker-compose.yml uses ${PROFILE:-release}. The published ghcr.io/base/node image is built with maxperf (build-release.yml), so the row now says the default is release and how to match the image.

Notes to reviewers

• entrypoint: https://github.com/base/base/blob/main/etc/scripts/node/execution-entrypoint (lines 15-16 and 60-70)
• window default: https://github.com/base/base/blob/main/crates/execution/node/src/args.rs (DEFAULT_PROOFS_HISTORY_WINDOW_BLOCKS, proofs_history_window)
• compose: https://github.com/base/base/blob/main/docker-compose.yml

If you'd rather expose the window through the entrypoint on the base/base side, happy to reword this once that lands.

How has it been tested?

node scripts/lint-mdx.js docs/specifications/node-operators/run-a-node.mdx passes (0 errors, 0 warnings).

Screenshots

N/A (prose and one table cell; no layout change)

[cb-heimdall]

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