feat: durable event subscriptions store, cache, and routes (PUT-1673)

[Salazareo]

Stacked on DS/put-1675 — review only this PR's diff; merges bottom-up.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	93.82% ⬆️ +0.06%	25719 / 27412
🔵	Statements	92.03% ⬆️ +0.03%	27836 / 30246
🔵	Functions	90.03% ⬆️ +0.02%	4574 / 5080
🔵	Branches	80.61% ⬇️ -0.05%	18644 / 23127

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/backend/clients/database/SqliteDatabaseClient.ts	89.14% 🟰 ±0%	57.45% 🟰 ±0%	81.6% 🟰 ±0%	95.58% 🟰 ±0%	6, 9, 13, 16, 24-26, 32, 33, 34, 38-39, 44, 45, 46, 47, 48, 236-238, 486-489, 504
src/backend/controllers/index.ts	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%
src/backend/controllers/events/EventsController.ts	82.85%	48.09%	61.29%	90.27%	6, 24-26, 32, 33, 34, 38-39, 44, 45, 47, 110-112, 118-120
src/backend/controllers/events/limits.ts	100%	100%	100%	100%
src/backend/services/events/EventsService.ts	88.54%	76.04%	92.3%	92.66%	254-257, 323, 329-332, 335, 340-347, 353-356, 393, 424, 463-464, 479, 513, 515, 520, 541, 543, 565, 612, 617, 641, 646, 669, 700-704, 718-720, 756, 777, 800, 812, 872, 986, 1007, 1109, 1147-1149, 1160-1161
src/backend/services/events/subscriptionCache.ts	93.93%	96.29%	87.5%	96.42%	156, 164
src/backend/stores/index.ts	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%
src/backend/stores/events/DurableSubscriptionStore.ts	98%	90.14%	100%	98.9%	142, 146
src/backend/stores/events/EventSubscriptionStore.ts	96.93%	72.72%	100%	99.3%	272, 428, 441, 508, 512
src/backend/stores/events/types.ts	100%	100%	100%	100%

Generated in workflow #938 for commit 2cd0bba by the Vitest Coverage Report Action