chore: remove superseded TimeWindowPagination, refresh DM design doc

Review prep for the DM pagination branch:

- Delete commons TimeWindowPagination + its test: the early since-based
  time-window approach, referenced only by its own test and fully
  superseded by UntilLimitPager (until+limit, gap-proof). 212 lines a
  reviewer would otherwise study for nothing.
- Bring the design doc up to the final architecture: NIP-04 per-relay
  filter scoping, per-relay independent paging (no rounds) + in-stream
  markers for the convo, the round model still used by rooms/gift-wrap,
  the WindowLoadTracker backstops and tracksReqSends gating, the
  loadingMore-starts-false fix, and the DMPagination diagnostics map.
  Marks the obsolete time-slice section as superseded.

https://claude.ai/code/session_01B1fmmmX8JjQWH3amMLdvcW

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/relayClient/pagination/TimeWindowPagination.kt

@@ -1,87 +0,0 @@
-/*
- * Copyright (c) 2025 Vitor Pamplona
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to use,
- * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
- * Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
- * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
- * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-package com.vitorpamplona.amethyst.commons.relayClient.pagination
-
-import com.vitorpamplona.quartz.utils.TimeUtils
-
-/**
- * Tracks how far back in time a relay subscription should reach.
- *
- * Boot opens a small window (recent-first) so a screen becomes usable before the
- * whole history is fetched and decrypted. Each [loadMore] widens the floor backward
- * so scrolling pulls older history on demand.
- *
- * Only the lower bound ([since]) moves: the subscription stays open so new events
- * keep streaming live regardless of the window. The floor is requested in full on
- * every assembly (the value is small and bounded), which keeps the window robust
- * even if the in-memory note store evicts previously-loaded events under memory
- * pressure.
- *
- * The step can grow geometrically ([growthFactor] > 1) so an auto-fill loop that keeps
- * widening to fill a screen (or to confirm there is no older history) converges in a
- * handful of requests instead of crawling back a fixed slice at a time. [maxLookback]
- * is a hard floor: once [since] reaches it, [isExhausted] is true and there is nothing
- * older to ask for.
- */
-class TimeWindowPagination(
-    private val initialWindow: Long = ONE_WEEK_IN_SECONDS,
-    private val step: Long = ONE_WEEK_IN_SECONDS,
-    private val growthFactor: Long = 1L,
-    private val maxLookback: Long = TEN_YEARS_IN_SECONDS,
-) {
-    /** Epoch seconds; events older than this are not requested from relays. */
-    @Volatile
-    var since: Long = TimeUtils.now() - initialWindow
-        private set
-
-    @Volatile
-    private var currentStep: Long = step
-
-    private fun floor() = TimeUtils.now() - maxLookback
-
-    /** Widens the window backward by the current step, clamped at [maxLookback], then grows the step. */
-    fun loadMore() {
-        since = maxOf(floor(), since - currentStep)
-        if (growthFactor > 1L) currentStep *= growthFactor
-    }
-
-    /** Jumps straight to [maxLookback] so a single request pulls the entire history. */
-    fun loadAll() {
-        since = floor()
-    }
-
-    /** True once the window has reached [maxLookback] — there is no older history to request. */
-    fun isExhausted(): Boolean = since <= floor()
-
-    /** Resets the window back to the initial boot size, anchored at the current time. */
-    fun reset() {
-        since = TimeUtils.now() - initialWindow
-        currentStep = step
-    }
-
-    companion object {
-        const val ONE_WEEK_IN_SECONDS = TimeUtils.ONE_WEEK.toLong()
-
-        // Covers the entire history of Nostr (which began ~2021) with margin, so reaching it
-        // genuinely means "nothing older exists" rather than an arbitrary cutoff.
-        const val TEN_YEARS_IN_SECONDS = TimeUtils.ONE_YEAR.toLong() * 10
-    }
-}