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/calendar/cpi.html

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+<!-- Official BLS cpi September 2026 report, retrieved 2026-10-24. Relevant table cells only. -->
+<div id="bodytext"><table id="cpi_pressa"><tr><td></td><td>Seasonally adjusted changes from preceding month</td><td>Un- adjusted 12-mos. ended Sep. 2026</td></tr><tr><td>Mar. 2026</td><td>Apr. 2026</td><td>May 2026</td><td>Jun. 2026</td><td>Jul. 2026</td><td>Aug. 2026</td><td>Sep. 2026</td></tr><tr><td>All items</td><td>0.9</td><td>0.6</td><td>0.5</td><td>-0.4</td><td>0.1</td><td>0.4</td><td>0.6</td><td>3.7</td></tr><tr><td>Food</td><td>0.0</td><td>0.5</td><td>0.2</td><td>0.2</td><td>0.1</td><td>0.1</td><td>0.0</td><td>2.5</td></tr><tr><td>Food at home</td><td>-0.2</td><td>0.7</td><td>0.1</td><td>0.2</td><td>-0.1</td><td>0.0</td><td>-0.1</td><td>1.8</td></tr><tr><td>Food away from home ( 1 )</td><td>0.2</td><td>0.2</td><td>0.3</td><td>0.2</td><td>0.3</td><td>0.3</td><td>0.2</td><td>3.5</td></tr><tr><td>Energy</td><td>10.9</td><td>3.8</td><td>3.9</td><td>-5.7</td><td>-1.5</td><td>2.1</td><td>5.2</td><td>20.4</td></tr><tr><td>Energy commodities</td><td>21.3</td><td>5.6</td><td>6.7</td><td>-9.5</td><td>-2.9</td><td>4.2</td><td>9.3</td><td>35.3</td></tr><tr><td>Gasoline (all types)</td><td>21.2</td><td>5.4</td><td>7.0</td><td>-9.7</td><td>-2.9</td><td>3.9</td><td>9.1</td><td>34.2</td></tr><tr><td>Fuel oil</td><td>30.7</td><td>5.8</td><td>3.8</td><td>-9.2</td><td>-1.7</td><td>10.1</td><td>15.3</td><td>74.2</td></tr><tr><td>Energy services</td><td>0.4</td><td>1.6</td><td>0.4</td><td>-0.7</td><td>0.3</td><td>-0.4</td><td>0.1</td><td>4.6</td></tr><tr><td>Electricity</td><td>0.8</td><td>2.1</td><td>0.6</td><td>-1.0</td><td>0.1</td><td>-0.2</td><td>0.2</td><td>4.4</td></tr><tr><td>Utility (piped) gas service</td><td>-0.9</td><td>-0.1</td><td>-0.5</td><td>0.5</td><td>0.7</td><td>-1.1</td><td>-0.3</td><td>5.0</td></tr><tr><td>All items less food and energy</td><td>0.2</td><td>0.4</td><td>0.2</td><td>0.0</td><td>0.2</td><td>0.3</td><td>0.3</td><td>2.6</td></tr><tr><td>Commodities less food and energy commodities</td><td>0.1</td><td>0.0</td><td>-0.1</td><td>-0.1</td><td>0.2</td><td>0.1</td><td>0.3</td><td>0.7</td></tr><tr><td>New vehicles</td><td>0.1</td><td>-0.2</td><td>-0.3</td><td>0.0</td><td>0.1</td><td>0.3</td><td>0.2</td><td>0.6</td></tr><tr><td>Used cars and trucks</td><td>-0.4</td><td>0.0</td><td>0.1</td><td>-0.2</td><td>0.4</td><td>0.4</td><td>0.7</td><td>-1.5</td></tr><tr><td>Apparel</td><td>1.0</td><td>0.6</td><td>0.3</td><td>-0.6</td><td>0.1</td><td>0.0</td><td>0.3</td><td>3.4</td></tr><tr><td>Medical care commodities ( 1 )</td><td>-1.0</td><td>-0.4</td><td>-0.7</td><td>-0.2</td><td>-0.6</td><td>-0.2</td><td>-0.7</td><td>-3.3</td></tr><tr><td>Services less energy services</td><td>0.2</td><td>0.5</td><td>0.3</td><td>0.0</td><td>0.2</td><td>0.3</td><td>0.4</td><td>3.1</td></tr><tr><td>Shelter</td><td>0.3</td><td>0.6</td><td>0.3</td><td>0.1</td><td>0.1</td><td>0.3</td><td>0.4</td><td>3.2</td></tr><tr><td>Transportation services</td><td>0.6</td><td>0.3</td><td>-0.6</td><td>-0.3</td><td>0.3</td><td>0.5</td><td>0.6</td><td>2.7</td></tr><tr><td>Medical care services</td><td>0.0</td><td>0.0</td><td>0.5</td><td>-0.1</td><td>0.6</td><td>-0.2</td><td>0.3</td><td>2.5</td></tr><tr><td>Footnotes
+		 (1)  Not seasonally adjusted.</td></tr></table></div>