Nest Logger in main.ts; fix README routes, example and DB model

[Essther77-git]

Closes #1397
Closes #1398
Closes #1399
Closes #1400

• main.ts: startup messages go through new Logger('Bootstrap'); the Swagger URL in the message now says /v1/docs, which is where SwaggerModule.setup mounts it
• README: all endpoints and curl examples use /v1, with a table of the routes that exist today (count, content, report, moderator, stats)
• README: create-gist example sends content (plus ttlHours/authorAddress) as CreateGistDto requires
• README: Database Model rewritten from gist.entity.ts and the migrations, including nullability and defaults

Tests and build were not run.

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