Add official US and European collection and calendar storage

Collect official RSS and Atom summaries, preserve historical captures, and poll macro releases with bounded cadence and Retry-After handling. Separate news collectors from the economic calendar worker.

Track statistical periods, publication stages, first observations, revisions, and current official series. Include explicit migration files and isolated archive, parsing, and import tests; no migration or import is executed by this commit.

Keep dependency declarations and lockfile together for PDF archives and the upcoming captcha integration. Verify the staged snapshot with 90 focused tests.

backend/tests/fixtures/europe/boe_feed.xml

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+<rss version="2.0"><channel><title>Speeches</title><link>https://www.bankofengland.co.uk/rss/speeches</link><description>Speeches</description><language>en</language><item><guid isPermaLink="false">{52B84329-5132-45B4-A1DB-7769939D3EBA}</guid><link>https://www.bankofengland.co.uk/speech/2026/october/physical-shocks-and-economic-resilience-speech-by-james-talbot</link><title>Physical shocks and economic resilience: a central bank perspective − speech by James Talbot</title><description>Given at the 2nd Annual Conference on Sustainable Finance at the Banco de México on 21 October 2026</description><pubDate>Fri, 23 Oct 2026 10:00:00 +0100</pubDate></item><item><guid isPermaLink="false">{2FC1AD25-F08D-4B82-BAF4-4B3E39B5B115}</guid><link>https://www.bankofengland.co.uk/speech/2026/october/katharine-braddick-mansion-house-city-regulators-dinner-london</link><title>The PRA’s second decade − speech by Katharine Braddick</title><description>Given at Mansion House</description><pubDate>Thu, 22 Oct 2026 21:00:00 +0100</pubDate></item><item><guid isPermaLink="false">{42D78C43-29CD-4AE3-A194-43FD6C114A62}</guid><link>https://www.bankofengland.co.uk/speech/2026/october/megan-greene-speech-at-lse-economics-society-london</link><title>Learning about earnings: Can we rely on labour market slack to mitigate the latest supply shock? − speech by Megan Greene</title><description>Given at London School of Economics</description><pubDate>Tue, 20 Oct 2026 18:00:00 +0100</pubDate></item><item><guid isPermaLink="false">{34B6B008-4B89-4167-840A-D31B0408149E}</guid><link>https://www.bankofengland.co.uk/speech/2026/october/financial-innovation-dollar-dominance-and-their-uk-monetary-policy-implications</link><title>Financial innovation, dollar dominance and their UK monetary policy implications</title><description>Presented at the Jackson Hole Economic Policy Symposium: Financial Innovation — Implications for Payments and Policy in Jackson, Wyoming. 28th August 2026</description><pubDate>Fri, 16 Oct 2026 21:00:00 +0100</pubDate></item></channel></rss>