changelog: date 2.0.0 for the day it ships, and record the two fixes that landed after it

[erfnzdeh]

Merge this last. It is the commit immediately before git tag -a v2.0.0,
and it depends on #17 and #18 being in.

The 2.0.0 entry was written on 4 September and dated 4 September, and then
nothing tagged it. Two user-visible fixes have merged into main since and
neither is in the changelog, because the entry was already closed:

• daemon status encoding to {} for a stopped daemon (daemon status: say running=false when offline; upgrading notes for editable installs #16), so the one
  command that exists to say the daemon is down could not say it.
• chat.list repeating its first page because both dialog-cursor builders
  used access_hash=0 (chat.list: carry the access hash into the dialog cursor #17). 34 rows before, 600+ across six pages after, on
  a live 936-dialog account.

Since 2.0.0 was never published there is no released artefact to contradict,
so one entry is more honest than a 2.0.0 nobody could install plus a 2.0.1 the
next day. Both fixes go under ### Fixed and the heading takes the date the
tag is actually cut.

After this merges

git checkout main && git pull
git tag -a v2.0.0 -m "v2.0.0"
git push origin v2.0.0

release.yml from #18 does the rest: version agreement across the tag,
tlgr.__version__ and this heading; the acceptance suite against the tagged
tree; sdist and wheel; a clean-environment install of the wheel; then the
GitHub release with this section as its notes and both artefacts attached.